Field
Size
Comment
6. Terminator character
2 hex characters
ASCII carriage return
This field is an ASCII carriage return placed at the end of a command packet. This
character is not the newline character "\n", but can be used in string assign statements
as "\r". There is not a space between the checksum and terminator field.
Command packet example
Command to be sent is “0x01” - GET CONTROLLER MODEL
Serial address of the controller is 5.
Command packet
“~ 05 01 00<CR>” where “<CR>” is return carriage character.
Command packet in ASCII hexadecimal
“7e 20 30 35 20 30 31 20 30 30 0D”
Response to “0x01” - GET CONTROLLER MODEL
“05 OK 00 DIGITEL SPCe 46<CR>” Where “<CR>” is the return carriage
character.
Note:
Command checksum is set to “00” to bypass the checksum field verification by the
controller.
9.6.
Decoding the command packet
An SPCe operates in one of three modes: monitor, receive, and respond.
Receipt of data is interrupt driven or otherwise multiplexed, so other tasks
are performed by the unit’s microprocessor. When the controller receives a
command packet, it continues monitoring for new commands while the
current one is carried out.
1.
MONITOR: The controller monitors serial data traffic. When a “start”
character is detected, the controller changes to the RECEIVE MODE.
2.
RECEIVE: After receiving start, the controller tests subsequent characters
for a valid command packet. This mode must have a count down timer
associated with it, which is a predetermined time for a valid command
packet SPCe to be received. Furthermore, if another start character is
received while in this mode, (i.e. the first start character was actually part
of a command packet for a different device) the controller responds by
going back to the beginning of the RECEIVE mode with a fresh timer
setting. If a command packet is not received within the allowed time
frame or if the checksum does not match, the timer is disabled, the
packet is discarded, and the mode is reset back to MONITOR. Once a
command packet is received, the mode changes to RESPOND. The only
way the controller can get to a RESPOND is by receiving:
▪ a valid start character followed by a space,
▪ a 2-byte hex value matching the controller’s address followed by a space,
▪ at least one 2-character hex value command followed by a space,
04/2021 - ©Gamma
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900026_F
900026_F - Serial (J3) and ethernet (J2) operation
