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TS-3200 User's Manual
5 Serial Ports
The two PC compatible asynchronous serial ports provide a means to communicate with external serial
devices such as printers, modems, etc. Each is independently configured as a standard PC COM port
which is compatible with the National Semiconductor's NS16C450. COM1 appears in the I/O space at
3F8h and uses IRQ4. COM2 is located at 2F8h and uses IRQ3.
The COM ports use a master clock of 1.8519 MHz as compared to a standard clock of 1.8432 MHz.
This results in an error for all baud rates of .0047 (less than ½ %). The error is insignificant and this
clock value allows standard baud rate selections -- for example a divisor of 12 yields 9600 baud.
By changing an internal configuration register in the 386EX, the serial clock can be switched to 12.5
MHz (the processor clock divided by 2). This feature allows baud rates higher than 115 kbaud (up to
781 kbaud), as well as low error, non-standard lower baud rates (such as 24 kbaud). See Appendix F
for further information.
The COM ports may also be configured to use a DMA channel, which is handy when very high baud
rates are being used. When enabled, a DMA request is issued any time a serial port's receive buffer is
full or its transmit buffer is empty. This allows higher speed operation with much lower CPU overhead.
See the Intel 386EX User's Manual for further details.
5.1 Serial Port Configuration Registers
Because both serial ports are 100% PC compatible, software written for the PC that accesses serial
ports directly or through standard BIOS calls will work without modification on the TS-3200. The details
of the COM port internal registers are available in most PC documentation books or the data sheet for
the National Semiconductor NS16C450 may be consulted.
5.2 Serial Port Hardware
Each serial port has 4 lines buffered: the two data lines
and the CTS / RTS handshake pair. This is quite suffi-
cient to interface with the vast majority of serial devices.
The serial lines are routed to 10 pin headers labeled
COM1 and COM2. A serial adapter cable can be plugged
into the header to convert this into a standard DB9 male
connector. The pin out for the 10 pin header and DB9
male connector are listed below. The RTS signal also
drives the DTR pin on the serial ports; DTR is always the
same state as RTS. In addition, RTS is also used to
enable the RS-485 transmitter (see below for more
details).
5.3 RS-485 Support
An option is available to add support to COM1 for half-duplex RS-485. RS-485 drivers allow commu-
nications between multiple nodes up to 4000 feet (1200 meters) via twisted pair cable. Half-duplex
RS-485 requires one twisted pair plus a Ground connection. Full-duplex RS-485 is not supported on
the TS-3200. Full Duplex is supported by the TS-3300 and TS-5300 products.
For half-duplex operation, a single twisted pair is used for transmitting and receiving. The serial port's
RTS signal controls the RS-485 transmitter/receiver. When RTS is asserted true (bit 1 of the modem
control register = 1), the RS-485 transmitter is enabled and the receiver disabled. When RTS is
deasserted the transmitter is tri-stated (disabled) and the receiver is enabled. Since the transmitter and
receiver are never both enabled, the serial port UART does not receive the data transmitted. The
5V Power 10
[in]
CTS
[out]
RTS
RS-485 TX- / RX- *
Figure 1 - Serial Port Header and DB9 Pin-
out [signal direction is in brackets]
* RS-485 is optional
PLEASE NOTE: The serial port headers
use a non-standard numbering scheme.
This was done so the header pins would
have the same numbering as the corre-
sponding DB-9 pin; i.e. pin 8 (CTS) on
the header connects to pin 8 on the DB-9
8
Technologic Systems
5
GND
NC
9
4
DTR (RTS) [out]
8
3
TX data
7
2
RX data
6
1
RS-485 TX+ / RX+ *
05/21/2009
[out]
[in]
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