RS422 with Aprilare 8800

aldous

Hi,

I have one Aprilare 880 and need to direct connect to a NXI seral port. I put the following codes to confirm the communication before I write anything to control. However, when I turn on "internal messages", I saw non-stop string "HVAC_8800 recevied string:" (but there is no value character behind the string and buffer variable filled with 0 (in hex). I tested the Aprilare 8800 by connecting to a PC with RS232 and using RS232 to RS485 converter. I was able to communication and control the Aprilare 8800. I also, connected my PC to the NXI serial port (using the same RS232 to RS485 converter), I was able to send and receive string between PC and AMX serial port. Therefore, I don't think that it is hardware problem. Anyone has experience with this? Please help and thanks very much

---

Defind_start
CREATE_BUFFER HVAC_8800, HVAC_8800_Buffers
...
data_event [HVAC_8800]
{
online:
{
send_command HVAC_8800, 'SET BAUD 9600, N, 8, 1, 485 DISABLE'
send_string 0, "'HVAC_8800 Online'"
}
string:
{
send_string 0, "'HVAC_8800 recevied string', HVAC_8800_Buffers"
}
}

---

Thanks,
Aldous

ericmedley

Are you certain you have your AMX serial port wired for rs422 and not rs232? Everything you describe sounds like a wiring issue.

GregG

I've nearly always controlled these with direct connection to the AMX, not the 232 adapter. And in fact, they seem to control as 422, not 485 even though their docs say 485 in a lot of places. The one job where we used an adapter was very unreliable.

So treat A+/- on the Tstat like Tx +/- and B+/- like Rx +/- then wire them up direct to AMX. 422 "just works" on the nxi ports without a code change, just find a pinout and connect them.


Offhand I can't recall if they are labeled so that Tx is what A is sending, or what it expects to have plugged into it - I haven't done a lot of residential the past few years. But I do recall that getting A/B swapped won't break anything as long as you always connect + to + and - to - .

ericmedley

I believe the AMX duet module for this stat also has the wiring printouts in the Word Doc that comes with. Might be worth a look.

aldous

Thanks everyone.

I was using Pin 6 to 9 (corrected my typo) on AMX. As far as I know that these are the pins for RS422/485. I'm going to try again. But, I have some questions would like confirm:

1. Are the wiring for RS422 and RS485 the same? Do I need to connect the ground?
2. The way to tell AMX to use RS422 is by using "SET BAUD 9600, N, 8, 1, 485 DISABLE". Am I right?
3. For connecting Aprilare 8800 to AMX directly, do I need to setup any flow control on AMX?

Thanks again for everyone

Aldous

GregG

rs-422 and "4-wire" rs-485 both use 4 connections rx+ rx- tx+ tx- Hooking up ground is not needed. Use 485 DISABLE for these.

What i usually consider rs-485 is "2 wire" mode and just uses data+ and data- (tx and rx are bridged on the netlinx master) for transmit and receive on the same pair - this mode needs 485 ENABLE so the AMX master knows to pull the transmitter off the bus when it is not talking so it can listen for others.

For the aprilaire, use 4 wires, no flow, and 485 disable.

If you are using an old NXI the pins are (6-9):

6 TX + Transmit data - try connected to B+
7 TX - Transmit data - try connected to B-
8 RX + Receive data - try connected to A+
9 RX - Receive data - try connected to A-

ericmedley

I seem to remember you do need the ground connected on the Aprilaire. Also make sure the TStat is the newer version. We had irresolvable issues with the 1.1 version of the TStats.

DHawthorne

ericmedley wrote: »

I seem to remember you do need the ground connected on the Aprilaire. Also make sure the TStat is the newer version. We had irresolvable issues with the 1.1 version of the TStats.

Nope, have done it many times, ground not needed. In fact, last I talked to Aprilaire on the matter, they said don't use it. At most, if you have a shielded cable, connect it on one side only for a drain. But it's not needed for a signal ground.

However, back to the OP, I have also seen that exact problem many times, and it's usually a bad thermostat. Try with another if you can before pulling out your hair.