489
Communications Guide
Modbus Functions
Function Code 07: Read Device Status
Function Code 08: Loopback Test
Modbus Implementation: Read Exception Status
489 Implementation: Read Device Status
This function reads the selected device status. A short message length allows for rapid reading of status. The returned status byte has individual bits set to 1 or 0 depending on the slave device status. The 489 general status byte is shown below:
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B0 | 1 | TRIP relay operated = 1 |
| B4 | 5 | ALARM relay operated = 1 |
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B1 | 2 | AUXILIARY relay operated = 1 |
| B5 | 6 | SERVICE relay operated = 1 |
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B2 | 3 | AUXILIARY relay operated = 1 |
| B6 | Stopped = 1 | |
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B3 | 4 | AUXILIARY relay operated = 1 |
| B7 | Running = 1 | |
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Note that if status is neither stopped or running, the generator is starting.
Message Format and Example:
Request status from slave 11.
Master Transmission | Bytes | Example | Description |
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Slave Address | 1 | 0B | message for slave 11 |
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Function Code | 1 | 07 | read device status |
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CRC (low, high) | 2 | 47 42 | computed CRC error code |
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Slave Response | Bytes | Example | Description |
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Slave Address | 1 | 0B | message from slave 11 |
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Function Code | 1 | 07 | read device status |
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Device Status | 1 | 59 | status = 01011001b |
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CRC (low, high) | 2 | C2 08 | computed CRC error code |
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Modbus Implementation: Loopback Test
489 Implementation: Loopback Test
This function is used to test the integrity of the communication link. The 489 will echo the request.
Message Format and Example:
Loopback test from slave 11.
Master Transmission | Bytes | Example | Description |
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Slave Address | 1 | 0B | message for slave 11 |
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Function Code | 1 | 08 | loopback test |
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Diagnostic Code | 2 | 00 00 | must be 0000h |
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Data | 2 | 00 00 | must be 0000h |
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CRC (low, high) | 2 | E0 A1 | computed CRC error code |
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Slave Response | Bytes | Example | Description |
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Slave Address | 1 | 0B | message from slave 11 |
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Function Code | 1 | 08 | loopback test |
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Diagnostic Code | 2 | 00 00 | must be 0000h |
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Data | 2 | 00 00 | must be 0000h |
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CRC (low, high) | 2 | E0 A1 | computed CRC error code |
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