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?
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[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,

[WarPony]

Thanks Darrell

I see. I forgot to change the mode bit. Still learning.

I really need a setpoint temperature for the "smarter" HVAC thermistat I am working on. I think I will just use another 18B20 as my setpoint temp and not worry about the alarms.

[Darrel Taylor]

I really need a setpoint temperature for the "smarter" HVAC thermistat I am working on. I think I will just use another 18B20 as my setpoint temp and not worry about the alarms.

You lost me there.
Using another 18B20 as a setpoint, would make it a "Variable point".

If you want to make a thermostat, it's probably easiest to just read the temperature and compare it against the desired "setpoints" in your program.
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[WarPony]

Absolutely

I am entering a setpoint in the software and also going to have another 18B20 outside to give me the "variable setpoint". This way the system knows if it really needs to turn on or to just pause until it warms up or cools down

[Darrel Taylor]

AH HA! I see now.

Very good. Carry On.
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