0172601 JOHNSON MANUAL RELIEF PARTS PKG

Illustration 1 g00645777
Communication overview of the CCM
The CCM communicates with the host equipment via a standard RS-232C serial data link. The serial data link uses the M50 protocol to transfer data. The M50 commands allow the user to periodically request a broadcast of multiple engine parameters. The broadcast is used by host equipment for monitoring. Single parameter read commands and write commands allow the user to control the engine from the host device.The host equipment can create a maximum of eight lists. The lists are stored in non-volatile memory in the CCM. These lists contain multiple engine parameters that are broadcast to the host device from the CCM through the RS-232C network. The engine parameters are given a unique parameter identifier (PID). Refer to the Operation and Maintenance Manual, SEBU7014, "Parameter Identifiers for General Usage" under the Programming Section of this manual. The CCM provides the communication link between the host device and the engine.The M50 protocol command messages that are transmitted to the CCM must be ASCII format. The response to the command messages will always be returned in ASCII format. The responses to the broadcast can be sent in ASCII. The responses to the broadcast can also be sent in binary. The format of the response is determined by the particular Instruction Identifier (IID) that is being used.The command messages contain an Instruction Identifier (IID). All command messages and responses will have the following standard preamble.50xxyyzz . . . . . (IID specific data) . . . . xx is the module identifier of the sending module.
Table 1
XX Module
00 Customer device
61 CCM yy is the Instruction Identifier.
Table 2
yy IID Description
10 Broadcast Response, program using IID 13
11 Activate a Broadcast List.
12 Deactivate a Broadcast List.
13 Program a Broadcast List.
15 Status Response to IID 11, 12, 13, and 82
24 Single Parameter Read Request
25 Response to IID 24
34 Single Parameter Write Request
35 Response to IID 34.
82 Request to Broadcast Diagnostic Codes zz is the number of bytes in the message after this byte. zz does not include the checksum. This value will change depending on the data that is associated with the IID. Calculation for the Checksum
The checksum is an important part of the M50 message. By using the checksum, the integrity of the message is determined. The checksum is a 2's complement value of the summation of all the data bytes in the message. The message is a good message if all the bytes and the checksum add to zero (0).The following message is an example.5000358131C9The checksum for this message is C9. Although the message is sent in ASCII, the checksum must be calculated by using the hexadecimal values.
Table 3
Byte ASCII Value Hexadecimal Value
$50 $35 $30 $50
$00 $30 $30 $00
$35 $33 $35 $35
$81 $38 $31 $81
$31 $33 $31 $31
Total $xx37
Mask $0037
2's Complement $C9
Total $00 The value of the checksum is calculated by using only the hexadecimal values of the data bytes. The x's in the first total indicate numbers that should be disregarded. The checksum in this case is $C9.Note: Numbers that are preceded by $ are in hexadecimal form.