MPCe/LPCe Users Manual
30
Cabling
The MPCe and LPCe function as DTE (Data Terminal Equipment) devices. When the controller is connected to
another DTE device (such as a personal computer), a null modem serial cable is required to connect the devices.
The null modem cable swaps the signal and control lines so that receive and transmit are properly connected.
The controller is equipped with a nine-pin female (DCE) D-sub connector protruding from the chassis rear.
RS-485 allows communications over greater distances. RS-485 cables can be as long 1220 meters (4000 ft.)
while RS-232 lines are typically limited to between 15 and 30 meters (50 - 100 ft.). RS-422 is possible for Apple’s
Macintosh computers which utilizes this protocol. Protocol configuration is accomplished by DIP switch settings
completed by Gamma Vacuum.
Maximum operating baud rate is determined by cable length and the environment near the cable. External noise
sources and line loss degrade the signal. Twisted-pair cable should be used with signal wires twisted with ground
wires. Shielded cables also decrease the maximum transmission length but may be required for (electrically)
noisy environments. The baud rate should be adjusted on the controller to ensure viable communication.
Command Packet Structure
The command packet is made up of at least five fields and contains information needed for a remote controller to
perform a command. The minimum command packet (single command with no data) is 11 bytes long and
consists of the following fields:
<START CHAR> <space> <ADDRESS> <space> <COMMAND> <space> <CHECKSUM> <TERMINATOR>
1 byte
1 byte
2 byte
1 byte
2 byte
1 byte
2 byte
1 byte
