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.