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SPI Interface

The SPI interface gives access to all features of the CRMXchip. The interface consists of five 3.3V digital signals:

  • IRQ – Interrupt signal. Active low, configurable through the interrupt mask register

  • CS – SPI Chip select, active low

  • SCK – SPI clock input

  • MOSI – SPI data input

  • MISO – SPI data output

Interface description

Bit and byte order

The data on the SPI bus is clocked with most significant bit first. All multi-byte register data are sent in big-endian byte order.

Clock polarity

Data is valid in the low-to-high transition of SCK. This is also known as the clock being active high with valid data on the leading clock edge.

Maximum clock speed

The maximum clock speed supported by TiMo is 2MHz. Clock speeds above this limit may result in unexpected behavior.

Setup time

The SPI slave unit has a setup time of 4 μs after the high-to-low transition of the CS signal.

SPI operation

SPI transactions

All SPI transactions start with a high-to-low transition on the CS pin. The CS pin must be held low during the entire SPI transaction.

The IRQ_FLAGS register is always shifted out as the first byte of each transaction.

Example SPI transaction

SPI commands

All SPI command sequences, except for the NOP command, consist of two SPI transactions. The first transaction shall be one byte long, this is the command byte. The second transaction is the payload. The second transaction must not be started until the TiMo module has confirmed the command by a high-to-low transition on the IRQ pin. The first byte being sent to TiMo in the second transaction will be ignored, however it is suggested this byte is being sent as 0xFF. See below for an example full SPI command sequence.

NOTE: Bit 7 in the IRQ flags register MUST be observed. A ‘1’ in this bit means that the SPI slave module is unable to process the current transaction, and the full command sequence MUST be restarted – this means sending the command transaction again.

Example SPI command sequence with a pending IRQ when sequence started

The available SPI commands are listed in the table below.

Command Binary value Comment
WRITE_REG 01AA AAAA Write to a register. AAAAAA = 6 bit register address.
READ_REG 00AA AAAA Read from a register. AAAAAA = 6 bit register address.
READ_DMX 1000 0001 Read the latest received DMX values from the window set up by the DMX_WINDOW register.
READ_ASC 1000 0010 Read the latest received ASC frame.
WRITE_DMX 1001 0001 Write DMX to the internal DMX generation buffer.
NOP 1111 1111 No operation. Can be used as a shortcut to read the IRQ_FLAGS register.

Register map

All undefined bits in the table below shall be considered reserved for future use - don't care when read, write as 0.

Do not read or write undefined registers – doing so could result in undefined behavior.

Address (hex) Mnemonic Bit no. Type Reset value Description
00 CONFIG Configuration register
UART_EN 0 R/W 1 Enable UART output of DMX frames (required for RDM).
0 = Disabled, 1 = Enabled
RADIO_TX_RX_MODE 1 R/W - 0 = Receiver, 1 = Transmitter
RX_ENABLE 7 R/W 1 Enable wireless DMX operation.
0 = Enabled, 1 = Disabled
01 STATUS Status register
LINKED 0 R/W - 0 = Not linked, 1 = Linked to TX (or pairing)
Write 1 to unlink
RF_LINK 1 R 0 0 = No radio link, 1 = Active radio link
DMX 3 R 0 0 = No DMX available, 1 = DMX available
Reserved 4-6 - - Reserved for future use
UPDATE_MODE 7 R 0 0 = chip operational, 1 = In driver update mode
02 IRQ_MASK IRQ mask register
RX_DMX_IRQ_EN 0 R/W 0 Enable DMX frame reception interrupt
LOST_DMX_IRQ_EN 1 R/W 0 Enable loss of DMX interrupt
DMX_CHANGED_IRQ_EN 2 R/W 0 Enable DMX changed interrupt
RF_LINK_IRQ_EN 3 R/W 0 Enable radio link status change interrupt
ASC_IRQ_EN 4 R/W 0 Enable alternative start code interrupt
Reserved 6-7 - - Reserved for future use
03 IRQ_FLAGS IRQ flags register
RX_DMX_IRQ 0 R 0 Complete DMX frame received interrupt
LOST_DMX_IRQ 1 R 0 Loss of DMX interrupt
DMX_CHANGED_IRQ 2 R 0 DMX changed in DMX window interrupt
RF_LINK_IRQ 3 R 0 Radio link status change interrupt
ASC_IRQ 4 R 0 Alternative start code frame received interrupt
Reserved 6 - - Reserved for future use
SPI_DEVICE_BUSY 7 R 0 SPI slave device is busy and cannot comply with command. Command sequence MUST be restarted.
04 DMX_WINDOW Status register
WINDOW_SIZE 0-15 R/W 512 Length of DMX window
START_ADDRESS 16-31 R/W 0 Start address of DMX window
05 ASC_FRAME ASC frame info register
START_CODE 0-7 R 0 Start code of received ASC frame
ASC_FRAME_LENGTH 8-23 R 0 Length of received ASC frame (0-512)
06 LINK_QUALITY Radio link quality register
PDR 0-7 R - Packet delivery rate (display as %)
0 = 0%, 255 = 100%
10 VERSION Version register
DRIVER_VERSION 0-31 R - Driver software version
HW_VERSION 32-63 R - Hardware revision
33 UNIVERSE_COLOR Universe Color Register
RGB_VALUE 0-23 R - 24 bit RGB value for the universe color.

Interrupts

The IRQ pin is used to indicate that there is one (or more) pending interrupt that has been enabled through the IRQ_MASK register. The IRQ pin is also used to indicate that the SPI slave is ready to receive the second transaction of an ongoing SPI command sequence.

The IRQ pin will always go high (inactive) after a successful SPI transaction. If any interrupts are pending, or when the chip is ready for the second transaction in a SPI command sequence it will be indicated through a high-to-low transition on the IRQ pin.

RX_DMX_IRQ

Asserted when a complete DMX frame has been received. Cleared by issuing a READ_DMX command sequence.

LOST_DMX_IRQ

Asserted when DMX stream is lost. This may be an effect of losing radio link, or if DMX stream in to the transmitter is terminated (for instance the DMX cable to the transmitter is unplugged). Cleared by reading the STATUS register.

DMX_CHANGED_IRQ

Asserted when a complete DMX frame has been received and any slot within the DMX window has changed value. Cleared by issuing a READ_DMX command sequence.

RF_LINK_IRQ

Asserted whenever the state of the radio link has changed. This may be:

  • radio link is lost

  • radio link is established

  • receiver got paired to transmitter

  • receiver got unpaired from transmitter

Cleared by reading the STATUS register.

ASC_IRQ

Asserted when a complete ASC frame has been received. Cleared by reading the ASC_FRAME register.

DMX Window register

The DMX_WINDOW register is used for setting up the DMX window filtering function. Please refer to the section about DMX window on page 20 for more details.

Hardware revision

Hardware revision is a 32bit number that shall be translated into a string. It indicates the revision number of the TiMo module. For instance the 32 bit value in hexadecimal form 0x000A0001 corresponds to module revision “000A0001”.

Driver version

The driver version is a 32bit value that shall be translated into a string on the form X.Y.Z.Y where X is the most significant byte of the 32 bit version number and Y is the least significant byte. For instance the 32 bit value 0x01000103 shall be presented as 1.0.1.3 on any UI or in any written representation.