DIO protocol
Introduction
The protocol for the DIO, 3FETs, 7FETs, RELAY, BIGRELAY and Pushbutton will be explained on this page. Most functions apply to all boards, but some don't.
This page describes both the SPI and the I2C version. See SPI versus I2C protocols for the explanation about how the protocols work in general.
Please see this page for the default addresses.
Write Ports
On the DIO and related boards all ports just set a single value. So writing more than one byte to such a port is redundant. The last value is the one used. The DIO boards don't have any ports that are logically a stream of bytes. So writing more than one or two bytes is not encouraged.
The DIO, 3FETS and 7FETS boards define several ports:
| port | available on | function | |||
|---|---|---|---|---|---|
| DIO | 3/7FETs | RELAY and BIGRELAY | pushbutton | ||
| 0x10 | X | X | X | set all outputs (bit 0 is output 0, etc). | |
| 0x20 .. 0x27 | X | X | X | set one output (0x20 for output 0, 0x21 for output 1 etc) | |
| 0x30 | X | X | X | define pins as inputs or outputs. 0 means input, 1 means output. | |
| 0x40 | X | X | set current position. (32 bits) The current position will be "renamed" to the given value. No motor movement will occur. | ||
| 0x41 | X | X | set target position. (32 bits) The motor will start stepping (hopefully in the rigth direction) to go to this position. You can read the current position to see if it has arrived yet. | ||
| 0x42 | X | X | set relative position. (32 bits) The target position is adjusted with this number. | ||
| 0x43 | X | X | set stepdelay. (in tenths of a microsecond, default 200: 20ms between steps). (8bits) | ||
| 0x50 .. 0x57 | v1.1 and up | X | Set PWM value. 0x50: output 0, 0x51 output 1 etc. | ||
| 0x5f | v1.1 and up | X | Set PWM mask. PWM is enabled on the outputs, who's bit is high. send 0x01 as data, to enable PWM on output 0 | ||
| 0x70 .. 0x77 | v1.2 and up | Select which i/o is coupled to which ADC channel. See analog inputs | |||
| 0x80 | v1.2 and up | Set number of ADC channels to read | |||
| 0x81 | v1.2 and up | Set number of samples to add (we suggest using a power of 2) (two bytes) | |||
| 0x82 | v1.2 and up | Set number of bits to shift accumulated sample value | |||
| 0xf0 | X | X | X | X | change address. Requires a write to 0xf1 and 0xf2 first. |
| 0xf1 | X | X | X | X | write 0x55 here to start unlocking the change address register. |
| 0xf2 | X | X | X | X | write 0xaa here to unlock the change address register. |
All the above ports are read/write. I.e. if you read from that port, you will get the current value.
Read Ports
The DIO, 3FETS, and 7FETS boards support the following read ports:
| port | available on | function | |||
|---|---|---|---|---|---|
| DIO | 3/7FETs | RELAY | pushbutton | ||
| 0x01 | X | X | X | X | identification string. (terminated with 0). |
| 0x02 | X | X | X | X | read eeprom (serial number). |
| 0x10 | X | X | X | X | read all inputs |
| registers 0x14 - 0x17: Implemented in DIO 1.5 and up. | |||||
| 0x14 | X | "hasbeenlow". The signal has been seen "low" since you last read this register. | |||
| 0x15 | X | "hasbeenhigh". The signal has been seen "high" since you last read this register. | |||
| 0x16 | X | "hasgoneup" the signal has been seen to transition "UP" since you last read this register. | |||
| 0x17 | X | "hasgonedown" the signal has been seen to transition "DOWN" since you last read this register. | |||
| 0x20 .. 0x27 | X | X | read one input (0x20 for input 0, 0x21 for input 1 etc) | ||
| 0x40 | X | X | read current position. | ||
| 0x41 | X | X | read target position. | ||
| 0x43 | X | X | read stepdelay. (in tenths of a microsecond, default 200: 20ms between steps). | ||
| 0x50 | v1.1 and up | X | Return PWM value for output 0 | ||
| 0x51 | v1.1 and up | X | Return PWM value for output 1 | ||
| 0x52 | v1.1 and up | X | Return PWM value for output 2 | ||
| 0x53 | v1.1 and up | X | Return PWM value for output 3 | ||
| 0x54 | v1.1 and up | X | Return PWM value for output 4 | ||
| 0x55 | v1.1 and up | X | Return PWM value for output 5 | ||
| 0x56 | v1.1 and up | X | Return PWM value for output 6 | ||
| 0x5f | v1.1 and up | X | Return PWM mask. PWM is enabled on the outputs, who's bit is high. send 0x01 as data, to enable PWM on output 0 | ||
| 0x60.. 0x67 | v1.2 and up | Return analog value (2 bytes) | |||
| 0x68 .. 0x6f | v1.2 and up | Return added and bitshifted analog value (2 bytes) | |||
| 0x70 .. 0x77 | v1.2 and up | Return which i/o is coupled to which ADC channel | |||
| 0x80 | v1.2 and up | Return number of ADC channels to read | |||
| 0x81 | v1.2 and up | Return number of samples to add (two bytes) | |||
| 0x82 | v1.2 and up | Return number of bits to shift accumulated sample value | |||
Using the digital ports
Before using a port as an output, you have to set the "data direction register". This is done by writing to port 0x30. For the first output, the lowest bit has to be "1". For the second output the next bit and so on.
For boards that only have outputs, like 3fets, 7fets, relay and bigrelay, you still have to make the signals into outputs. So we recommend that you send a 0xff to register 0x30 in the initialization sequence.
Using the analog inputs
Taking measurements
The built-in ADC has 10 bits of resolution, and can be read in two different ways:
- Just read the latest sample
- Add x samples, and optionally bitshift the result by n bits.
The first option is easy, but prone to some noise.
The second option gives you the ability to reduce the noise and/or obtain higher resolution.
To take the average of a number of samples, set the "nsamp" (0x81) register to 2^n, and set the shift (0x82) register to n. This tells the controller to sum 2^n samples, and then divide by 2^n, resulting in the average value, which can be read from registers 0x68 .. 0x6f, depending on the channel.
For more than 10 bits of precision, it's possible to skip the bitshifting. In theory, this gives you a higher accuracy than the ADC's 10 bits. To do this, set register 0x81 to 2^n, and set register 0x82 to 0. The result can then be read from registers 0x68 .. 0x6f, depending on the channel. Do take note that statisticians have proven that you gain only n/2 of significant bits this way.
You can set nsamp (register 0x81) to 4096 (0x1000 = 2^12), and then the shift register (0x82) to 6. This will give you a 16bit results with about 16 bits of significance. The performance is such that you can get an update about every second in this mode. This is ideal for things like temperature readings.
Setting up the ADC
First decide which i/o pins you want to use as analog inputs, and which i/o pin is analog 0, 1, etc. These settings need to be written to registers 0x70 .. 0x76, 0x70 being analog0, and 0x76 being analog6. The following values are valid:
| IO pin | value |
|---|---|
| 0 | 0x07 |
| 1 | 0x03 |
| 2 | analog not available |
| 3 | 0x02 |
| 4 | 0x01 |
| 5 | analog not available |
| 6 | 0x00 |
The measurements are done with the 5V power supply rail as the "full scale" reference voltage. You can use an internal 1.1V reference voltage by adding 0x80 to the values in the table above.
Now decide how you want to sample the analog values, and set those registers.
Finally, you need to write the amount of analog channels you want to use to register 0x80. The controller wil now start sampling those channels.
ADC Example
We want to use IO 4 and IO 0 for reading analog values, and want an average value over 16 samples. To do this, we need to send the following commands:
| command | explanation |
|---|---|
| 0x84 0x70 0x01 | Couple ADC channel 0 to IO4 |
| 0x84 0x71 0x07 | Couple ADC channel 1 to IO0 |
| 0x84 0x81 0x00 0x01 | Add 256 (2^8) samples |
| 0x84 0x82 0x04 | Bitshift result by 4 bits |
| 0x84 0x80 0x02 | Set number of channels to sample to 2 |
Now you can read from ADC channel 0 and 1:
| command | explanation |
|---|---|
| 0x85 0x68 0xXX 0xXX | read channel 0, for SPI send the bytes XX, get the data on the MISO line. For I2C, just read two bytes after sending the other bytes. |
| 0x85 0x69 0xXX 0xXX | read channel 1. |
PWM Example
We want to use IO 4 and IO 0 for PWM, and then set IO 0 to 20% and IO4 to 50%:
| command | explanation |
|---|---|
| 0x84 0x5f 0x11 | bitmask of the IOs that use PWM: Add 0x01 for IO0 and 0x10 for IO4. |
| 0x84 0x50 0x33 | 20% of 255 is 51 = 0x33. |
| 0x84 0x54 0x80 | 50% of 255 is 128 = 0x80. |
examples
For SPI in the examples below, "data sent" means the data on the MOSI line, while "data received" means the data on the MISO line. when MISO reads "xx" you should ignore the data. When MOSI reads "xx" it doesn't matter what you send.
For I2C in the examples below, you should first initiate a "write" transaction with the data in the "data sent column". Don't send the "xx" bytes. Then you initiate a "read" transaction, and you will get the data in the "data received" column (and again not the "xx" bytes).
read identification
read the identification string of the board. (SPI_DIO)
| data sent | data received | explanation |
|---|---|---|
| 0x85 | xx | select destination with address 0x84 for READ. |
| 0x01 | xx | identify |
| xx | 0x73 | 's' |
| xx | 0x70 | 'p' |
| xx | 0x69 | 'i' |
| xx | ... | etc. |
read the identification string of the board. (I2C_DIO)
| I2C master | I2C slave (i2c_dio) | explanation |
|---|---|---|
| START | -- | start I2C transaction |
| 0x84 | -- | select destination with address 0x84 for write (set port). |
| 0x01 | -- | identify |
| STOP | -- | terminate I2C transaction. |
| START | -- | start I2C transaction |
| 0x85 | -- | select destination with address 0x84 for READ. |
| -- | 0x69 | 'i' |
| -- | 0x32 | '2' |
| -- | 0x63 | 'c' |
| -- | ... | etc. |
Note that in the SPI example, there is bidirectional datatransfer on every cycle, but the data is "don't care" or "must ignore" (indicated by xx), while in the I2C case, the other side cannot send as there is only one data-transfer direction (indicated by "--").
turn on all outputs
| data sent | data recieved | explanation |
|---|---|---|
| 0x88 | xx | select destination with address 0x88 for WRITE |
| 0x10 | xx | set outputs as in bitpattern (next byte) |
| 0xff | xx | All outputs active. |
turn on output 4
| data sent | data recieved | explanation |
|---|---|---|
| 0x88 | xx | select destination with address 0x88 for WRITE |
| 0x24 | xx | port 0x24: output 4... |
| 0xff | xx | ... active. |
move stepper to step 0x1234
| data sent | data recieved | explanation |
|---|---|---|
| 0x88 | xx | select destination with address 0x88 for WRITE |
| 0x41 | xx | port 0x41: set target position |
| 0x34 | xx | low byte |
| 0x12 | xx | high byte. |
example script for rpi
This script assumes that you have "bw_tool" installed on your rpi. Actually, it will work on any Linux machine that has I2C support.
This script moves a single "on" state back and forth along the outputs. If you connect a "DIO_LEDS", you'll see the led move up and down.
#!/bin/sh t=0.1 addr=84 dio="bw_tool -I -D /dev/i2c-1 -a $addr " # # Set all pins as outputs. $dio -W 30:ff:b # while true ; do # I'm lazy. didn't write a proper loop. Sorry. $dio -W 10:01:b sleep $t $dio -W 10:02:b sleep $t $dio -W 10:04:b sleep $t $dio -W 10:08:b sleep $t $dio -W 10:10:b sleep $t $dio -W 10:20:b sleep $t $dio -W 10:40:b sleep $t $dio -W 10:20:b sleep $t $dio -W 10:10:b sleep $t $dio -W 10:08:b sleep $t $dio -W 10:04:b sleep $t $dio -W 10:02:b sleep $t done