This project is to create a GPIO expander that takes read and write commands over SPI.
The maximum SPI frequency is 2.5mhz.
- 1: Write bit 1 = write | 0 = read
- 1: Address size bit 1 = 8 bit address | 0 = 16 bit address
- 1: Address high bit set zero 1 = set address high to zero | 0 = reuse previous address high
- 5: read/write length
The address is also read out before it is written
| Write 3 bytes with 16 bit address | Write 2 bytes with 8 bit address |
| 0x83 | 0x-- | 0x-- | 0x-- | 0x-- | 0x-- | 0xC2 | 0x-- | 0x-- | 0x-- | 0x-- |
MOSI: | Command | Address | Address | Write | Write | Write | Command | Address | Write | Write | N/A | N/A |
MISO: | N/A | N/A | N/A | N/A | N/A | Read | Read | Read | N/A | N/A | Read | Read |
A command can be sent during the last pad byte of the read command
| Read 3 bytes with 16 bit address | Read 2 bytes with 8 bit address |
| 0x03 | 0x-- | 0x-- | 0x-- | 0x-- | 0x62 | 0x-- | 0x-- | 0x-- | 0x-- |
MOSI: | Command | Address | Address | N/A | N/A | Command | Address | N/A | N/A | N/A | N/A |
MISO: | N/A | N/A | N/A | N/A | N/A | Read | Read | Read | N/A | Read | Read |
To setup anlog pin reader. send this command
0x83 //write 3 bytes to 8 bit address with high byte = 0
0x1C //address low
0xE0 //enable analog pins 5-7
0x01 //analog enable pins 8, 10-15
0x8F //analog accumulate to 16 bits and reset accumulator
Setup and start the ADC (See ATTiny427 datasheet for more information)
0x85 //write 5 bytes to 16 bit address
0x06 //address high
0x00 //address low
0b00100001; // enable ADC with low latency
0x01 // prescaler DIV4 to get ADCCLK 5MHZ
0xA0 // set timebase and VDD as reference
0x00 // no window source mode
0x01 //enable RESRDY intterupt
0xC3 //write 3 bytes to 8 bit address using existing high byte
0x08 //address low
0x05 //SAMPDUR = 5. this give a sample duration of 4us
0x00 //no accumulation, accumulation done in software so the readings are evenly spaced
0x11 //single 12 bit mode and start
Read the result at address 0x340E. There is also a rolling sample counter at 0x340D
Results for Timer B capture interrupts are stored here
0x3400 TCB0_Count
0x3401 TCB0_CNT
0x3403 TCB0_CCMP
0x3405 TCB1_Count
0x3406 TCB1_CNT
0x3408 TCB1_CCMP
Refer to datasheet for how to setup Timer B
Timer B can be setup to parse incoming SENT data from a sensor To setup SENT pin reader. send this command
0x81 //write 1 bytes to 8 bit address with high byte = 0
0x1E //address low
0x60 //This is shared with AnalogAccumulate register. bit 5 and 6 are the SENT decoder enabled for Timer B 0 and 1 respectively
//Care should be taken to not overwrite any of the analog enable bits.
Results are stored here
0x3400 TCB0_Count
0x3401 TCB0_SENT
0x3405 TCB1_Count
0x3406 TCB1_SENT
If writing to the PORT_DIR register. make sure the MISO line is set as output. MISO is PA2 or PC1 if using alternate SPI