1-Wire

[WarPony]

Can anyone help me with the syntax for writing to a one-wire devices scratch pad?
I want to set the Th, Tl, and config bytes (byte 3,4,5).

I was thinking

Owout PortX.X, 1, [$CC, $4E] 'skip ROM search and write to scratch pad
Owout PortX.X, 1, [$XX, $XX,$XX] bytes 3, 4, and 5

Do I need place holders for the first to two bytes on the scratch pad? If so, what is that syntax?

[Darrel Taylor]

It looks like you are using a DS18B20.
It's best to include that kind of information with the questions.
If not then this won't apply.

DS1820 resolution
http://www.picbasic.co.uk/forum/showthread.php?p=47692

[WarPony]

Thanks old chap

i have been beating my head into the wall

I understand the alarm registers are 8 bit with the MSB being the sign bit. Is that a straight decimal conversion? i.e. 25 degrees Celsius would be %00011001

Again

Thanks a lot

[Darrel Taylor]

Sure, that'll work. Added: (not the beating your head part)
Or you could just use 25.

OWOUT DQ, 1, [$CC, $4E, 25, 0]

High limit = 25°C
Low limit = 0°C

If you want to use negative alarms, it's easier to use a variable

LowLimit   VAR BYTE
HighLimit  VAR BYTE

HighLimit = 20
LowLimit = -10

OWOUT DQ, 1, [$CC, $4E, HighLimit, LowLimit]

Do you know how to read the alarm status yet?
<br

[WarPony]

Think so

How's this?

Alarm_H VAR Bit
Alarm_L Var Bit

Owout DQ, 1, [$CC, $EC]
Owin DQ, 1, [Alarm_H, Alarm_L]

Is it going to send back a 1 or 0 alarm bit?

[Darrel Taylor]

Think so

How's this?

Well, not so good.

There is only 1 Alarm status bit, No SkipROM, and mode 4 (bit data) is used to retrieve it after the AlarmSearch command.

Alarm   VAR BIT

OWOUT   DQ, 1, [$EC]
OWIN    DQ, 4, [Alarm]

If there is an alarm, you have to read the temperature to figure out whether it's too high or too low.

It will return a 0 if there is an alarm, 1 if not. But you can reverse that easily with...

Alarm = Alarm ^ 1

hth,