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SERIAL PORTS CHAPTER 4

Page 12 RPC-30

Figure 4-1 Serial ports

DESCRIPTION

The RPC -30 has two serial ports that can be used for

interfacing to a printer, terminal, RS-485 network, or

other ser ial devices. This chapte r descr ibes their

characteristics and how to use them. Frequent

references are m ade to commands listed in the

CAMBA SIC Programming Manual. P lease ref er to this

manual for more infor mation about these com mands.

Serial por ts are num bered C OM 1 and CO M2. COM 1 is

used for program development. During run time, it can

be used for other functions. C OM2 is a general purpose

port and can be used as either RS-232 or RS-422/485.

Both ports support XO N/XOF F protocol to contr ol data

transmission. Each por t has a 256 character interrupt

driven input and output buffer. This allows charac ters to

be sent out (using PRINT) without slowing down

program execution. However, if the PRINT buffer fills,

program execution is suspended until the buffer em pties.

Both ports have a 256 character input buffer. When

more than 256 characters have been received, excess

ones are ignored.

The baud rate, parity, data length, and stop bit length are

changed using the CONFIG BAUD command.

COM1 SERIAL PORT

This port uses a VTC-9F serial cable to connect external

serial devices to the port. The cable consists of a 10 pin

IDC connector wired one-to-one to a DB-9 connector.

Line 10 is sim ply cut off. The pinout is designed so it

plugs directly into the 9 pin serial port connector on a

PC.

COM 1 does not use hardware handshake lines. T he

CTS line is pulled high in case external equipment uses

this line.

This port is normally used for program ming. D uring

run time it may be used as a general purpose seria l port.

When used for programming or with the INPUT

statement, it will accept ASCII character values from 0

to 127. When used with the INKEY$ and COM$

functions, it will return ASCII values from 0 to 255.

COM2 SERIAL PORT

COM 2 is either an RS-232 or RS-422/485 port. It also

uses a VTC-9F serial cable, described above, for RS-232

level communications. COM2 is identical to COM1

except that COM 2 has 2 hardware handshaking lines,

CTS and RTS. W hen RTS goes low, the RPC -30 is held

off from transmitting out COM2. The status of this port

is read by the BIT statement. The example below

returns the status of the RTS line:

100 B = BIT(194,5)

If B = 1, transmission is held off.

The CTS line may be set high or low to hold off

comm unication. Line 400 sets CTS low and 500 sets it

high.

400 BIT 192,4,1

500 BIT 192,4,0

Jumper W5 determines if COM 2 is RS-232 or RS-

422/485.

[1-2] RS-485

[2-3] RS-232 (default)

The CONFIG BAUD statement sets the configuration of

this port.

Termination network

When the RPC-30 is the last physical unit on a network,

or it is the only unit (RS-422), the receiver m ust be

terminated to prevent ring ing. Jumper block W4 installs

or removes this network. Set W4 according to the table

below:

[1-3],[2-4] Termination network installed

[3-5],[4-6] Termination network removed

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 ... 37 38

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