TWIM — I2C compatible two-wire interface master with EasyDMA

TWI master with EasyDMA (TWIM) is a two-wire half-duplex master which can communicate with multiple slave devices connected to the same bus

Listed here are the main features for TWIM:

I²C compatible
100 kbps, 250 kbps, or 400 kbps
Support for clock stretching
EasyDMA

The two-wire interface can communicate with a bi-directional wired-AND bus with two lines (SCL, SDA). The protocol makes it possible to interconnect up to 127 individually addressable devices. TWIM is not compatible with CBUS.

The GPIOs used for each two-wire interface line can be chosen from any GPIO on the device and are independently configurable. This enables great flexibility in device pinout and efficient use of board space and signal routing.

Figure 1. TWI master with EasyDMA

A typical TWI setup consists of one master and one or more slaves. For an example, see Figure 2. This TWIM is only able to operate as a single master on the TWI bus. Multi-master bus configuration is not supported.

Figure 2. A typical TWI setup comprising one master and three slaves

This TWI master supports clock stretching performed by the slaves. The TWI master is started by triggering the STARTTX or STARTRX tasks, and stopped by triggering the STOP task. The TWI master will generate a STOPPED event when it has stopped following a STOP task.

The TWI master cannot get stopped while it is suspended, so the STOP task has to be issued after the TWI master has been resumed.

After the TWI master is started, the STARTTX task or the STARTRX task should not be triggered again before the TWI master has stopped, i.e. following a LASTRX, LASTTX or STOPPED event.

If a NACK is clocked in from the slave, the TWI master will generate an ERROR event.

Shared resources

The TWI master shares registers and other resources with other peripherals that have the same ID as the TWI master. Therefore, you must disable all peripherals that have the same ID as the TWI master before the TWI master can be configured and used.

Disabling a peripheral that has the same ID as the TWI master will not reset any of the registers that are shared with the TWI master. It is therefore important to configure all relevant registers explicitly to secure that the TWI master operates correctly.

The Instantiation table in Instantiation shows which peripherals have the same ID as the TWI.

EasyDMA

The TWI master implements EasyDMA for reading and writing to and from the RAM.

If the TXD.PTR and the RXD.PTR are not pointing to the Data RAM region, an EasyDMA transfer may result in a HardFault or RAM corruption. See Memory for more information about the different memory regions.

The .PTR and .MAXCNT registers are double-buffered. They can be updated and prepared for the next RX/TX transmission immediately after having received the RXSTARTED/TXSTARTED event.

The STOPPED event indicates that EasyDMA has finished accessing the buffer in RAM.

EasyDMA list

EasyDMA supports one list type.

The supported list type is:

Array list

EasyDMA array list

The EasyDMA array list can be represented by the data structure ArrayList_type.

For illustration, see the code example below. This data structure includes only a buffer with size equal to Channel.MAXCNT. EasyDMA will use the Channel.MAXCNT register to determine when the buffer is full. Replace 'Channel' by the specific data channel you want to use, for instance 'NRF_SPIM->RXD', 'NRF_SPIM->TXD', 'NRF_TWIM->RXD', etc.

The Channel.MAXCNT register cannot be specified larger than the actual size of the buffer. If Channel.MAXCNT is specified larger than the size of the buffer, the EasyDMA channel may overflow the buffer.

This array list does not provide a mechanism to explicitly specify where the next item in the list is located. Instead, it assumes that the list is organized as a linear array where items are located one after the other in RAM.

      
  #define BUFFER_SIZE  4
  
  typedef struct ArrayList
  {
    uint8_t buffer[BUFFER_SIZE];
  } ArrayList_type;

  ArrayList_type MyArrayList[3];

  //replace 'Channel' below by the specific data channel you want to use,
  //         for instance 'NRF_SPIM->RXD', 'NRF_TWIM->RXD', etc.
  Channel.MAXCNT = BUFFER_SIZE;
  Channel.PTR = &MyArrayList;

Figure 3. EasyDMA array list

Master write sequence

A TWI master write sequence is started by triggering the STARTTX task. After the STARTTX task has been triggered, the TWI master will generate a start condition on the TWI bus, followed by clocking out the address and the READ/WRITE bit set to 0 (WRITE=0, READ=1).

The address must match the address of the slave device that the master wants to write to. The READ/WRITE bit is followed by an ACK/NACK bit (ACK=0 or NACK=1) generated by the slave.

After receiving the ACK bit, the TWI master will clock out the data bytes found in the transmit buffer located in RAM at the address specified in the TXD.PTR register. Each byte clocked out from the master will be followed by an ACK/NACK bit clocked in from the slave.

A typical TWI master write sequence is illustrated in Figure 4. Occurrence 2 in the figure illustrates clock stretching performed by the TWI master following a SUSPEND task.

A SUSPENDED event indicates that the SUSPEND task has taken effect; this event can be used to synchronize the software.

Figure 4. TWI master writing data to a slave

The TWI master will generate a LASTTX event when it starts to transmit the last byte, this is illustrated in Figure 4

The TWI master is stopped by triggering the STOP task, this task should be triggered during the transmission of the last byte to secure that the TWI will stop as fast as possible after sending the last byte. It is safe to use the shortcut between LASTTX and STOP to accomplish this.

Note that the TWI master does not stop by itself when the whole RAM buffer has been sent, or when an error occurs. The STOP task must be issued, through the use of a local or PPI shortcut, or in software as part of the error handler.

The TWI master cannot get stopped while it is suspended, so the STOP task has to be issued after the TWI master has been resumed.

Master read sequence

A TWI master read sequence is started by triggering the STARTRX task. After the STARTRX task has been triggered the TWI master will generate a start condition on the TWI bus, followed by clocking out the address and the READ/WRITE bit set to 1 (WRITE = 0, READ = 1). The address must match the address of the slave device that the master wants to read from. The READ/WRITE bit is followed by an ACK/NACK bit (ACK=0 or NACK = 1) generated by the slave.

After having sent the ACK bit the TWI slave will send data to the master using the clock generated by the master.

Data received will be stored in RAM at the address specified in the RXD.PTR register. The TWI master will generate an ACK after all but the last byte received from the slave. The TWI master will generate a NACK after the last byte received to indicate that the read sequence shall stop.

A typical TWI master read sequence is illustrated in Figure 5. Occurrence 2 in the figure illustrates clock stretching performed by the TWI master following a SUSPEND task.

A SUSPENDED event indicates that the SUSPEND task has taken effect; this event can be used to synchronize the software.

The TWI master will generate a LASTRX event when it is ready to receive the last byte, this is illustrated in Figure 5. If RXD.MAXCNT > 1 the LASTRX event is generated after sending the ACK of the previously received byte. If RXD.MAXCNT = 1 the LASTRX event is generated after receiving the ACK following the address and READ bit.

The TWI master is stopped by triggering the STOP task, this task must be triggered before the NACK bit is supposed to be transmitted. The STOP task can be triggered at any time during the reception of the last byte. It is safe to use the shortcut between LASTRX and STOP to accomplish this.

Note that the TWI master does not stop by itself when the RAM buffer is full, or when an error occurs. The STOP task must be issued, through the use of a local or PPI shortcut, or in software as part of the error handler.

The TWI master cannot get stopped while it is suspended, so the STOP task has to be issued after the TWI master has been resumed.

Figure 5. The TWI master reading data from a slave

Master repeated start sequence

A typical repeated start sequence is one in which the TWI master writes two bytes to the slave followed by reading four bytes from the slave. This example uses shortcuts to perform the simplest type of repeated start sequence, i.e. one write followed by one read. The same approach can be used to perform a repeated start sequence where the sequence is read followed by write.

The figure Figure 6 illustrates this:

Figure 6. A repeated start sequence, where the TWI master writes two bytes followed by reading 4 bytes from the slave

If a more complex repeated start sequence is needed and the TWI firmware drive is serviced in a low priority interrupt it may be necessary to use the SUSPEND task and SUSPENDED event to guarantee that the correct tasks are generated at the correct time. This is illustrated in Figure 7.

Figure 7. A double repeated start sequence using the SUSPEND task to secure safe operation in low priority interrupts

Low power

When putting the system in low power and the peripheral is not needed, lowest possible power consumption is achieved by stopping, and then disabling the peripheral.

The STOP task may not be always needed (the peripheral might already be stopped), but if it is sent, software shall wait until the STOPPED event was received as a response before disabling the peripheral through the ENABLE register.

Master mode pin configuration

The SCL and SDA signals associated with the TWI master are mapped to physical pins according to the configuration specified in the PSEL.SCL and PSEL.SDA registers respectively.

The PSEL.SCL and PSEL.SDA registers and their configurations are only used as long as the TWI master is enabled, and retained only as long as the device is in ON mode. When the peripheral is disabled, the pins will behave as regular GPIOs, and use the configuration in their respective OUT bit field and PIN_CNF[n] register. PSEL.SCL, PSEL.SDA must only be configured when the TWI master is disabled.

To secure correct signal levels on the pins used by the TWI master when the system is in OFF mode, and when the TWI master is disabled, these pins must be configured in the GPIO peripheral as described in Table 1.

Only one peripheral can be assigned to drive a particular GPIO pin at a time. Failing to do so may result in unpredictable behavior.

Table 1. GPIO configuration before enabling peripheral
TWI master signal	TWI master pin	Direction	Output value	Drive strength
SCL	As specified in PSEL.SCL	Input	Not applicable	S0D1
SDA	As specified in PSEL.SDA	Input	Not applicable	S0D1

Registers

Table 2. Instances
Base address	Peripheral	Instance	Description	Configuration
0x40003000	TWIM	TWIM0	Two-wire interface master 0
0x40004000	TWIM	TWIM1	Two-wire interface master 1

Table 3. Register Overview
Register	Offset	Description
TASKS_STARTRX	0x000	Start TWI receive sequence
TASKS_STARTTX	0x008	Start TWI transmit sequence
TASKS_STOP	0x014	Stop TWI transaction. Must be issued while the TWI master is not suspended.
TASKS_SUSPEND	0x01C	Suspend TWI transaction
TASKS_RESUME	0x020	Resume TWI transaction
EVENTS_STOPPED	0x104	TWI stopped
EVENTS_ERROR	0x124	TWI error
EVENTS_SUSPENDED	0x148	Last byte has been sent out after the SUSPEND task has been issued, TWI traffic is now suspended.
EVENTS_RXSTARTED	0x14C	Receive sequence started
EVENTS_TXSTARTED	0x150	Transmit sequence started
EVENTS_LASTRX	0x15C	Byte boundary, starting to receive the last byte
EVENTS_LASTTX	0x160	Byte boundary, starting to transmit the last byte
SHORTS	0x200	Shortcut register
INTEN	0x300	Enable or disable interrupt
INTENSET	0x304	Enable interrupt
INTENCLR	0x308	Disable interrupt
ERRORSRC	0x4C4	Error source
ENABLE	0x500	Enable TWIM
PSEL.SCL	0x508	Pin select for SCL signal
PSEL.SDA	0x50C	Pin select for SDA signal
FREQUENCY	0x524	TWI frequency
RXD.PTR	0x534	Data pointer
RXD.MAXCNT	0x538	Maximum number of bytes in receive buffer
RXD.AMOUNT	0x53C	Number of bytes transferred in the last transaction
RXD.LIST	0x540	EasyDMA list type
TXD.PTR	0x544	Data pointer
TXD.MAXCNT	0x548	Maximum number of bytes in transmit buffer
TXD.AMOUNT	0x54C	Number of bytes transferred in the last transaction
TXD.LIST	0x550	EasyDMA list type
ADDRESS	0x588	Address used in the TWI transfer

SHORTS

Address offset: 0x200

Shortcut register

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																							F		D	C	B	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	LASTTX_STARTRX										Shortcut between LASTTX event and STARTRX task See EVENTS_LASTTX and TASKS_STARTRX
			Disabled	0								Disable shortcut
			Enabled	1								Enable shortcut
B	RW	LASTTX_SUSPEND										Shortcut between LASTTX event and SUSPEND task See EVENTS_LASTTX and TASKS_SUSPEND
			Disabled	0								Disable shortcut
			Enabled	1								Enable shortcut
C	RW	LASTTX_STOP										Shortcut between LASTTX event and STOP task See EVENTS_LASTTX and TASKS_STOP
			Disabled	0								Disable shortcut
			Enabled	1								Enable shortcut
D	RW	LASTRX_STARTTX										Shortcut between LASTRX event and STARTTX task See EVENTS_LASTRX and TASKS_STARTTX
			Disabled	0								Disable shortcut
			Enabled	1								Enable shortcut
F	RW	LASTRX_STOP										Shortcut between LASTRX event and STOP task See EVENTS_LASTRX and TASKS_STOP
			Disabled	0								Disable shortcut
			Enabled	1								Enable shortcut

INTEN

Address offset: 0x300

Enable or disable interrupt

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id											J	I			H	G	F									D								A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	STOPPED										Enable or disable interrupt for STOPPED event See EVENTS_STOPPED
			Disabled	0								Disable
			Enabled	1								Enable
D	RW	ERROR										Enable or disable interrupt for ERROR event See EVENTS_ERROR
			Disabled	0								Disable
			Enabled	1								Enable
F	RW	SUSPENDED										Enable or disable interrupt for SUSPENDED event See EVENTS_SUSPENDED
			Disabled	0								Disable
			Enabled	1								Enable
G	RW	RXSTARTED										Enable or disable interrupt for RXSTARTED event See EVENTS_RXSTARTED
			Disabled	0								Disable
			Enabled	1								Enable
H	RW	TXSTARTED										Enable or disable interrupt for TXSTARTED event See EVENTS_TXSTARTED
			Disabled	0								Disable
			Enabled	1								Enable
I	RW	LASTRX										Enable or disable interrupt for LASTRX event See EVENTS_LASTRX
			Disabled	0								Disable
			Enabled	1								Enable
J	RW	LASTTX										Enable or disable interrupt for LASTTX event See EVENTS_LASTTX
			Disabled	0								Disable
			Enabled	1								Enable

INTENSET

Address offset: 0x304

Enable interrupt

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id											J	I			H	G	F									D								A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	STOPPED										Write '1' to Enable interrupt for STOPPED event See EVENTS_STOPPED
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
D	RW	ERROR										Write '1' to Enable interrupt for ERROR event See EVENTS_ERROR
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
F	RW	SUSPENDED										Write '1' to Enable interrupt for SUSPENDED event See EVENTS_SUSPENDED
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
G	RW	RXSTARTED										Write '1' to Enable interrupt for RXSTARTED event See EVENTS_RXSTARTED
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
H	RW	TXSTARTED										Write '1' to Enable interrupt for TXSTARTED event See EVENTS_TXSTARTED
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
I	RW	LASTRX										Write '1' to Enable interrupt for LASTRX event See EVENTS_LASTRX
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
J	RW	LASTTX										Write '1' to Enable interrupt for LASTTX event See EVENTS_LASTTX
			Set	1								Enable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled

INTENCLR

Address offset: 0x308

Disable interrupt

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id											J	I			H	G	F									D								A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	STOPPED										Write '1' to Disable interrupt for STOPPED event See EVENTS_STOPPED
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
D	RW	ERROR										Write '1' to Disable interrupt for ERROR event See EVENTS_ERROR
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
F	RW	SUSPENDED										Write '1' to Disable interrupt for SUSPENDED event See EVENTS_SUSPENDED
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
G	RW	RXSTARTED										Write '1' to Disable interrupt for RXSTARTED event See EVENTS_RXSTARTED
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
H	RW	TXSTARTED										Write '1' to Disable interrupt for TXSTARTED event See EVENTS_TXSTARTED
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
I	RW	LASTRX										Write '1' to Disable interrupt for LASTRX event See EVENTS_LASTRX
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled
J	RW	LASTTX										Write '1' to Disable interrupt for LASTTX event See EVENTS_LASTTX
			Clear	1								Disable
			Disabled	0								Read: Disabled
			Enabled	1								Read: Enabled

ERRORSRC

Address offset: 0x4C4

Error source

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																	C	B	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	OVERRUN										Overrun error A new byte was received before previous byte got transferred into RXD buffer. (Previous data is lost)
			NotReceived	0								Error did not occur
			Received	1								Error occurred
B	RW	ANACK										NACK received after sending the address (write '1' to clear)
			NotReceived	0								Error did not occur
			Received	1								Error occurred
C	RW	DNACK										NACK received after sending a data byte (write '1' to clear)
			NotReceived	0								Error did not occur
			Received	1								Error occurred

ENABLE

Address offset: 0x500

Enable TWIM

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	ENABLE										Enable or disable TWIM
			Disabled	0								Disable TWIM
			Enabled	6								Enable TWIM

PSEL.SCL

Address offset: 0x508

Pin select for SCL signal

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id				B																											A	A	A	A	A
Reset 0xFFFFFFFF				1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1
Id	RW	Field	Value Id	Value								Description
A	RW	PIN		[0..31]								Pin number
B	RW	CONNECT										Connection
			Disconnected	1								Disconnect
			Connected	0								Connect

PSEL.SDA

Address offset: 0x50C

Pin select for SDA signal

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id				B																											A	A	A	A	A
Reset 0xFFFFFFFF				1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1
Id	RW	Field	Value Id	Value								Description
A	RW	PIN		[0..31]								Pin number
B	RW	CONNECT										Connection
			Disconnected	1								Disconnect
			Connected	0								Connect

FREQUENCY

Address offset: 0x524

TWI frequency

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id				A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x04000000				0	0	0	0	0	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	FREQUENCY										TWI master clock frequency
			K100	0x01980000								100 kbps
			K250	0x04000000								250 kbps
			K400	0x06400000								400 kbps

RXD.PTR

Address offset: 0x534

Data pointer

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id				A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	PTR										Data pointer

RXD.MAXCNT

Address offset: 0x538

Maximum number of bytes in receive buffer

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																												A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	MAXCNT		[1..255]								Maximum number of bytes in receive buffer

RXD.AMOUNT

Address offset: 0x53C

Number of bytes transferred in the last transaction

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																												A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	R	AMOUNT										Number of bytes transferred in the last transaction. In case of NACK error, includes the NACK'ed byte.

RXD.LIST

Address offset: 0x540

EasyDMA list type

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	LIST										List type
			Disabled	0								Disable EasyDMA list
			ArrayList	1								Use array list

TXD.PTR

Address offset: 0x544

Data pointer

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id				A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	PTR										Data pointer

TXD.MAXCNT

Address offset: 0x548

Maximum number of bytes in transmit buffer

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																												A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	MAXCNT		[1..255]								Maximum number of bytes in transmit buffer

TXD.AMOUNT

Address offset: 0x54C

Number of bytes transferred in the last transaction

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																												A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	R	AMOUNT										Number of bytes transferred in the last transaction. In case of NACK error, includes the NACK'ed byte.

TXD.LIST

Address offset: 0x550

EasyDMA list type

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																																	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	LIST										List type
			Disabled	0								Disable EasyDMA list
			ArrayList	1								Use array list

ADDRESS

Address offset: 0x588

Address used in the TWI transfer

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Id																													A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Id	RW	Field	Value Id	Value								Description
A	RW	ADDRESS										Address used in the TWI transfer

Electrical specification

TWIM interface electrical specifications

Symbol	Description	Min.	Typ.	Max.	Units
f_TWIM	Bit rates for TWIM¹	100		400	kbps
I_TWIM,100kbps	Run current for TWIM, 100 kbps		50		µA
I_TWIM,400kbps	Run current for TWIM, 400 kbps		50		µA
t_{TWIM,START,LP}	Time from STARTRX/STARTTX task to transmission started, Low power mode		t_{TWIM,START,CL} + t_{START_HFINT}		µs
t_{TWIM,START,CL}	Time from STARTRX/STARTTX task to transmission started, Constant latency mode		1.5		µs

Two Wire Interface Master (TWIM) timing specifications

Symbol	Description	Min.	Typ.	Units
f_{TWIM,SCL,100kbps}	SCL clock frequency, 100 kbps		100	kHz
f_{TWIM,SCL,250kbps}	SCL clock frequency, 250 kbps		250	kHz
f_{TWIM,SCL,400kbps}	SCL clock frequency, 400 kbps		400	kHz
t_{TWIM,SU_DAT}	Data setup time before positive edge on SCL – all modes	300		ns
t_{TWIM,HD_DAT}	Data hold time after negative edge on SCL – all modes	500		ns
t_{TWIM,HD_STA,100kbps}	TWIM master hold time for START and repeated START condition, 100 kbps	10000		ns
t_{TWIM,HD_STA,250kbps}	TWIM master hold time for START and repeated START condition, 250kbps	4000		ns
t_{TWIM,HD_STA,400kbps}	TWIM master hold time for START and repeated START condition, 400 kbps	2500		ns
t_{TWIM,SU_STO,100kbps}	TWIM master setup time from SCL high to STOP condition, 100 kbps	5000		ns
t_{TWIM,SU_STO,250kbps}	TWIM master setup time from SCL high to STOP condition, 250 kbps	2000		ns
t_{TWIM,SU_STO,400kbps}	TWIM master setup time from SCL high to STOP condition, 400 kbps	1250		ns
t_{TWIM,BUF,100kbps}	TWIM master bus free time between STOP and START conditions, 100 kbps	5800		ns
t_{TWIM,BUF,250kbps}	TWIM master bus free time between STOP and START conditions, 250 kbps	2700		ns
t_{TWIM,BUF,400kbps}	TWIM master bus free time between STOP and START conditions, 400 kbps	2100		ns

Figure 8. TWIM timing diagram, 1 byte transaction

Figure 9. Recommended TWIM pullup value vs. line capacitance

The I2C specification allows a line capacitance of 400 pF at most.
The nRF52832 internal pullup has a fixed value of typ. 13 kOhm, see R_PU in the GPIO chapter.

¹ Higher bit rates or stronger pull-ups may require GPIOs to be set as High Drive, see GPIO chapter for more details.