Serial Communication; Flow Control; Wiring Configuration - Global Cache GC-100-06 Quick Start Manual

communication utilizes a male (9 pin) DB9 connector with active signals on the pins shown in the diagram.
Serial
Unfortunately, serial standards are not always adhered to, and special attention must be given when connecting serial cables.
There are three areas that must be correct for proper serial communication: cable configuration; baud rate (communication
speed); and, if used, flow control signals must be asserted (greater than +3V). At a minimum, to send and receive serial data
TxD, RxD, and Gnd must be connected to the other serial device. These signal locations will depend on the mating connector's
type and gender. Typically, communications can be established by a trial and error method of swapping the TxD and RxD
lines. (Incorrect wiring will not harm RS232 drivers.) Also, flow control must be disabled or asserted for communications to
start. If erroneous characters are transmitted, it is usually an indication of an incorrect baud rate setting.
DTR +12V
CTS
TxD
RTS
RxD
Serial DB9 Male Connector
There are two types of flow control: RTS/CTS for data flow and DTR/DSR for modem control. The GC-100 does not use
modem flow control and will always assert the DTR line and ignore DSR. When data flow control is used, the GC-100 will
stop its transmission when its CTS signal is asserted by the other device. When receiving data the GC-100 may assert RTS to
signal the other device to stop its transmission. In a typical control environment, serial devices usually communicate with short
and infrequent commands. Hence, some serial devices may not have flow control signals. This is usually not a concern, since a
serial input buffer is much larger (256 bytes) than the transmitted data commands. In these cases, the GC-100 flow control
should be disabled. However, to avoid potential character loss, it is a good rule to use flow control when it is available on serial
devices. The GC-100 performs flow control by asserting RTS when the input buffer goes beyond 192 bytes, and de-asserting
RTS when it falls below 64 bytes. In either case, the GC-100 records all serial buffer overflows and maintains a count on the
Network web page.
The serial device attaching to the GC-100 will most likely employ a DB9 or 25 pin connector. Below is the standard wiring
configuration for a serial cable. It is not guaranteed that the standard has been followed, but it is a good starting place.
C-100 DB9 DB9
DB9 male male female
Data
RxD 2 3 2
TxD 3 2 3
Gnd 5 5 5
Data Flow Control
RTS 7 8 7
CTS 8 7 8
Modem Controls
DTR 4 6 4
DSR 6 ignored by the GC-100
GC-100-06 Quick Start Guide - PDF
Effective: January 18, 2007
PN: 030127-02 pdf ver. 10
2 of 3
Pin 5
Pin 4
Pin 8
Pin 3
Pin 7
Pin 2
DB25 DB25
male female
3 2
2 3
7 7
5 4
4 5
6 20
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