POWER protocol
Introduction
The protocol for the POWER board will be explained on this page.
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
The POWER boards define several ports:
| port | function |
|---|---|
| 0x20 | set the turn-off-time. 32-bits, in ms. This is an offset into the future. So specify 4000 to turn off in 4 seconds. |
| 0x21 | set the turn-on-time. 32-bits, in ms. Specify e.g. 600000 to turn the system back on in 10 minutes. This starts counting as soon as you set it. |
| 0xf0 | change address. Requires a write to 0xf1 and 0xf2 first. |
| 0xf1 | write 0x55 here to start unlocking the change address register. |
| 0xf2 | 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 | function |
|---|---|
| 0x01 | identification string. (terminated with 0). |
| 0x02 | read eeprom (serial number). |
| 0x20 | read the turn-off-time left. 32-bits, in ms. |
| 0x21 | read the turn-on-time left. 32-bits, in ms. |
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_POWER)
| data sent | data received | explanation |
|---|---|---|
| 0xa5 | 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_POSER)
| 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 ten minutes from now
| data sent | data recieved | explanation | |||||||
|---|---|---|---|---|---|---|---|---|---|
| 0xa4 | xx | select destination with address 0xa4 for WRITE | |||||||
| 0x21 | xx | port address: set turn-on-time | |||||||
| 0xc0 | xx | lowest byte of 600000 ms = 0x927c0 ms is 0xc0. | - | 0x27 | xx |
- |
0x09 | xx | |
| 0x00 | xx | MSB. |
turn off four seconds from now
(on your raspberry pi you can do this from your /etc/init.d/halt script just before the "halt -d -f ..." command. )
| data sent | data recieved | explanation | |||||||
|---|---|---|---|---|---|---|---|---|---|
| 0xa4 | xx | select destination with address 0xa4 for WRITE | |||||||
| 0x20 | xx | port address: set turn-on-time | |||||||
| 0xa0 | xx | lowest byte of 4000 ms = 0xfa0 ms is 0xa0. | - | 0x0f | xx |
- |
0x00 | xx | |
| 0x00 | xx | MSB. |