Imp <-> RS-485

Yeah, you can’t create const arrays in squirrel, you’d have to do:

wCRCTable <- [ 0x0000, 0x1021… (etc) ];

This works fine though, and I’ve done similar stuff for forming CRCs in squirrel before now.

Thanks. Taking a bit of getting used to the initialization.
Here is the full modbus CRC16 creation

wCRCTable <- [
0x0000, 0xC0C1, 0xC181, 0x0140, 0XC301, 0X03C0, 0X0280, 0XC241,
0XC601, 0X06C0, 0X0780, 0XC741, 0X0500, 0XC5C1, 0XC481, 0X0440,
0XCC01, 0X0CC0, 0X0D80, 0XCD41, 0X0F00, 0XCFC1, 0XCE81, 0X0E40,
0X0A00, 0XCAC1, 0XCB81, 0X0B40, 0XC901, 0X09C0, 0X0880, 0XC841,
0XD801, 0X18C0, 0X1980, 0XD941, 0X1B00, 0XDBC1, 0XDA81, 0X1A40,
0X1E00, 0XDEC1, 0XDF81, 0X1F40, 0XDD01, 0X1DC0, 0X1C80, 0XDC41,
0X1400, 0XD4C1, 0XD581, 0X1540, 0XD701, 0X17C0, 0X1680, 0XD641,
0XD201, 0X12C0, 0X1380, 0XD341, 0X1100, 0XD1C1, 0XD081, 0X1040,
0XF001, 0X30C0, 0X3180, 0XF141, 0X3300, 0XF3C1, 0XF281, 0X3240,
0X3600, 0XF6C1, 0XF781, 0X3740, 0XF501, 0X35C0, 0X3480, 0XF441,
0X3C00, 0XFCC1, 0XFD81, 0X3D40, 0XFF01, 0X3FC0, 0X3E80, 0XFE41,
0XFA01, 0X3AC0, 0X3B80, 0XFB41, 0X3900, 0XF9C1, 0XF881, 0X3840,
0X2800, 0XE8C1, 0XE981, 0X2940, 0XEB01, 0X2BC0, 0X2A80, 0XEA41,
0XEE01, 0X2EC0, 0X2F80, 0XEF41, 0X2D00, 0XEDC1, 0XEC81, 0X2C40,
0XE401, 0X24C0, 0X2580, 0XE541, 0X2700, 0XE7C1, 0XE681, 0X2640,
0X2200, 0XE2C1, 0XE381, 0X2340, 0XE101, 0X21C0, 0X2080, 0XE041,
0XA001, 0X60C0, 0X6180, 0XA141, 0X6300, 0XA3C1, 0XA281, 0X6240,
0X6600, 0XA6C1, 0XA781, 0X6740, 0XA501, 0X65C0, 0X6480, 0XA441,
0X6C00, 0XACC1, 0XAD81, 0X6D40, 0XAF01, 0X6FC0, 0X6E80, 0XAE41,
0XAA01, 0X6AC0, 0X6B80, 0XAB41, 0X6900, 0XA9C1, 0XA881, 0X6840,
0X7800, 0XB8C1, 0XB981, 0X7940, 0XBB01, 0X7BC0, 0X7A80, 0XBA41,
0XBE01, 0X7EC0, 0X7F80, 0XBF41, 0X7D00, 0XBDC1, 0XBC81, 0X7C40,
0XB401, 0X74C0, 0X7580, 0XB541, 0X7700, 0XB7C1, 0XB681, 0X7640,
0X7200, 0XB2C1, 0XB381, 0X7340, 0XB101, 0X71C0, 0X7080, 0XB041,
0X5000, 0X90C1, 0X9181, 0X5140, 0X9301, 0X53C0, 0X5280, 0X9241,
0X9601, 0X56C0, 0X5780, 0X9741, 0X5500, 0X95C1, 0X9481, 0X5440,
0X9C01, 0X5CC0, 0X5D80, 0X9D41, 0X5F00, 0X9FC1, 0X9E81, 0X5E40,
0X5A00, 0X9AC1, 0X9B81, 0X5B40, 0X9901, 0X59C0, 0X5880, 0X9841,
0X8801, 0X48C0, 0X4980, 0X8941, 0X4B00, 0X8BC1, 0X8A81, 0X4A40,
0X4E00, 0X8EC1, 0X8F81, 0X4F40, 0X8D01, 0X4DC0, 0X4C80, 0X8C41,
0X4400, 0X84C1, 0X8581, 0X4540, 0X8701, 0X47C0, 0X4680, 0X8641,
0X8201, 0X42C0, 0X4380, 0X8341, 0X4100, 0X81C1, 0X8081, 0X4040];

function CRC16calc(msg_blob, msgLength){
local nTemp;
local wCRCWord = 0xFFFF;
local nData = 0;

while (msgLength–) {
nTemp = 0xff & (msg_blob[nData++] ^ wCRCWord);
wCRCWord = 0xffff& (wCRCWord >> 8);
wCRCWord = wCRCWord ^ wCRCTable[nTemp];

return wCRCWord;

I’m trying to add the crc word on the back of a message and getting a funny error - of course maybe there is an easy way of adding the 16bit word on.
ERROR: the index ‘writen’ does not exist
ERROR: at modBusTxSync:164
ERROR: from entryTimer:266
local wCrcWord= CRC16calc(rtuReq_blob, rtuReq_blob.len()); local crcLsb =(0xff&wCrcWord); local crcMsb = (0xff&(wCrcWord>>8)); local txBuf_blob = blob(rtuMsgLen+2); txBuf_blob = rtuReq_blob;// want to crcLsb +crcMsb; txBuf_blob.writen(crcLsb,'b'); << Error

So, you shouldn’t be creating a blob then assigning it like that - the empty blob you created will just be thrown away on assignment, I believe. However, I’m not sure whether the assignment is working right there… Peter may have to comment.

If the last 2 lines are:

txBuf_blob.writeblob(rtuReq_blob); txBuf_blob.writen(crcLsb,'b');

…does that work?

Weell the following compiles, but gives me a runtime ERROR: invalid type tag
function modBusTxSync(rtuReq_blob,rtuMsgLen){ local wCrcWord= CRC16calc(rtuReq_blob, rtuMsgLen); txBuf_blob=blob.writeblob(rtuReq_blob); << err: invalid type tag txBuf_blob.writen(wCrcWord,'w');
which I’m calling from
const rtuRdDataReq_blob = "\\x01\\x03\\x00\\x04\\x00\\x01\\xc5\\xcb"; ... modBusTxSync(rtuRdDataReq_blob,rtuRdDataReq_blob.len());

Because rtuRdDataReq_blob isn’t a blob – it’s a string. Use txBuf_blob.writestring() instead?


Ok, thanks for the hint about the ‘invalid type tag’ - now I see its not a string :). However
local txBuf_blob=blob.writestring(rtuReq_blob); >>ERROR: the index 'writestring' does not exist
or trying
local txBuf_blob=blob(20); txBuf_blob.writestring(rtuReq_blob);>>ERROR: the index 'writestring' does not exist
If I look up
I can’t see a .writestring() - though I like the idea.
The following doesn’t cause any runttime issues
local txBuf_blob=blob(20); txBuf_blob.writen(crcLsb, 'b');

Oh, whoops, blob.writestring is an Electric Imp extension to Squirrel, and while it’s in the next imp firmware release, it’s not in the current one. Until then, turning a string s into a blob b looks like this:
local b = blob(s.len()); foreach (c in s) b.writen(c, 'b');


Wonderful that works for me. Thanks very much.
Great to hear some interesting extensions ~ I’d throw in my 2cents for some documentation that covers all the EI extensions. Looking at the wiki it would be describes the librarys extensions - currently I try searching everything to see if a keyword exists.
I’ve pushed out the basic Modbus program