MPCe/LPCe Users Manual
29
Serial Interface, J112
J112 is a 9-pin, female DE-9 connector that routes serial interface signals. Specific protocols are configured at
the factory. The default setting is RS 232. Alternate configurations are RS 485 (full or half duplex) and RS 422.
Specific OEM configurations may also be available upon request.
RS-232 Operation
RS-485 Operation
RS-422 Operation
DCD
1
+TX
2
+RX
3
RXD
2
–TX
8
–RX
7
TXD
3
GND
5
GND
5
GND
5
DSR
6
RTS
7
CTS
8
TIA/EIA RS-232/422/485 are electrical standards specifying hardware requirements for a serial communications
interfaces. The standard specifies a bi-directional (half duplex), multi-point interface, allowing multiple devices to
be connected to the same serial port on a computer. The standard does not set up or address any software
protocols. A carefully planned protocol for use between the remote devices and the controlling computer allows
devices manufactured by different companies to function on the same port, even if they do not use the same
protocol. This section lays out a standard protocol for use on any future Gamma Vacuum instruments that use the
standard, and makes recommendations regarding hardware design in areas where software performance may be
affected.
Standard
The interface consists of a differential (balanced) twisted wire pair that is connected to all devices on that serial
port. This makes the interface fairly immune to electrical and RF (radio frequency) noise generated in the vicinity.
All controllers on the same port must be configured for the same baud rate.
Devices cannot send data until they have been addressed by the controlling computer. A typical command
exchange for a device would be:
1. The computer sends a command.
2. Devices read the address.
3. When a device recognizes its address, it decodes the message and returns an acknowledgement to the
computer, along with any data that was requested.
The serial communications port settings such as number of data/start/stop bits, parity, etc. are defined
subsequently. Every communications exchange between the controlling computer and a Gamma Vacuum
controller using the standard interface consists of a command packet (sent by the controlling computer), and a
response packet (returned by the remote controller). All characters in these packets are ASCII. All fields are
separated by a space (not required between the checksum and terminator). Hexadecimal numbers can be
represented in either upper or lower case.
