© 2009 Cypress Solutions
Complete Manual: CTM-15X Firmware 1.2.0
(Revision 1.0)
139
9BMODBUS Messages
Reg.
#
Register content
Notes
0 – 5
Analog input 1 to 6
values
Value in volts x 100
6
Modem supply Vcc
volts x 100
7
Modem 1xRTT RSSI
value
signed integer – units dBm
8
Modem internal
temperature
signed integer – units degrees Celsius
9
GPS day & month
HEX
10
GPS year
Signed integer
11
GPS hours & minutes
HEX
12
GPS seconds & GPS
validity flag
Validity flag: A = valid; V = invalid
13 –
14
GPS Latitude
Floating point radian format. To convert to degrees multiply by 180/pi
(negative numbers are South, positive are North)
15 –
16
GPS Longitude
Floating point radian format. To convert to degrees multiply by 180/pi
(negative numbers are West, positive are East)
17
GPS speed
Value in m/sec x 10
18
GPS heading
Value 0 to 359 degrees (integer)
10.5
Error response
If the modem is not able to correctly respond to a request then it will send an error response.
Error response format:
0xII 0x8N 0xXX 0xZZ 0xZZ
Where:
0xII
is the modem’s assigned MODBUS ID
0x8N
is the error code corresponding with the request:
0x81
is for read coils
0x82
is for read discrete inputs
0x84
is for read input registers
0x85
is for write coil
0xXX
is the exception code: 0x01, 0x02, 0x03, or 0x04
0xZZ
0xZZ is the CRC checksum for this message
10.6
MODBUS TCP Messages
MODBUS TCP messages are identical to those used with standard MODBUS except that they drop the two
byte CRC check sum at the end of every message.