All ConnectWare data link layer frames transmitted over any of the three serial interfaces by either the CWM or OKE will be in the following format:
Field | SOF | CMD | TID | LEN | PAYLOAD | CRC16 |
Byte Size | 1 | 1 | 1 | 1 | LEN | 2 |
Value | 0x01 | 0-255 | 0-255 | 0-240 | Variable | 0-65535 |
All multibyte integer values are in Big Endian network byte order (most significant byte first).
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The following are the currently defined CMD values:
Name | Value | Description |
Unacknowledged Commands (0x00-0x0F) | ||
ACK | 0x00 | Acknowledges successful frame reception and that payload will be processed. Does not indicate if the payload was processed successfully or not. |
NACK | 0x01 | Indicates successful frame reception, however the payload was not processed. |
Acknowledged Commands | ||
BUS | 0x10 | Indicates the master is allowing the slave to transmit on the RS-485 bus. The PAYLOAD is empty. |
DATA_REQ | 0x11 | Indicates the PAYLOAD is data for the receiver to process. |
TID
The Transaction ID field, TID, shall follow the CMD field. It may have a value from 0 to 255 and is 1 byte in size.
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When the CWM has not yet established communication with its OKE then the CWM shall enter a discovery mode where it will attempt to determine which physical interface and what communication settings must be used between it and the of the attached OKE.
The discovery sequence is:
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Use no parity, 8 data bits, and 1 stop bit for all discovery attempts.
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On TTL RS-232 port send an OKM PING and look for a matching OKM PING using 9600, 19200, 38400, 57600, 115200, and 230400 baud rates.
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On RS-485 port send an OKM PING and look for a matching OKM PING using 9600, 19200, 38400, 57600, 115200, and 230400 baud rates.
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Baud/Port Settings | Port |
|---|---|
38400 N81 | TTL |
NA | USB |
115200 N81 | RS-232 |
115200 N81 | RS-485 |
115200 N81 | TTL |
9600 N81 | RS-232 |
9600 N81 | RS-485 |
9600 N81 | TTL |
19200 N81 | RS-232 |
19200 N81 | RS-485 |
19200 N81 | TTL |
38400 N81 | RS-232 |
38400 N81 | RS-485 |
57600 N81 | RS-232 |
57600 N81 | RS-485 |
57600 N81 | TTL |
230400 N81 | RS-232* |
230400 N81 | RS-485 |
230400 N81 | TTL |
Note: CWM1 does not support 230400 baud on its RS-232 port and will not discover devices on that port at that baud rate.
Each port/baud combination will be pinged once every 5 seconds up to 4 times. If the 4th ping is not replied to, the next port/baud combination will be scanned.
Use no parity, 8 data bits, and 1 stop bit for all discovery attempts.
When a matching OKM PING is received on any interface the discovery procedure will stop immediately.
If the discovery sequence fails to find the ConnectWare equipment, then the module will idle for 10 seconds, and retry the discovery sequence. The complete discovery sequence loop takes about 8 minutes.
| Note |
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The module must receive a link layer ping response and a network layer ping response to complete discovery. |
When the module finds the equipment port and settings it will save these settings to non-volatile memory and will not initiate discovery again, unless its configuration is reset, or it is commanded to do so explicitly.
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