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SERIAL PORTS CHAPTER 4

Page 10 RPC-150

Figure 4-1 Serial ports

DESCRIPTION

The RPC -150 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 information.

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

COM 1 is J1 and is called the Console port on the card.

This port uses a VTC-10 serial cable to connect external

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

IDC connector wired to a DB-9 connector. T he

connector plugs directly into a 9 pin serial port connector

on a PC.

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

COM2 is an RS-232 port. It also uses a VTC-10 serial

cable, described above. COM2 is identical to COM1

except that COM 2 has 2 hardware handshaking lines,

CTS and RTS. W hen RTS goes low, the RPC -150 is

held off from transmitting out C OM2. T he status of this

port is read by the BIT statement. The exam ple below

returns the status of the RTS line:

100 B = BIT(130,5)

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 128,4,1

500 BIT 128,4,0

The CONFIG BAUD statement sets the configuration of

this port.

ACCESSING SERIAL BUFFERS

You can access C OM1 and COM 2 buffers in three w ays:

1. INPUT sta tement. This removes all characters in

the buffer up to the term inator cha racter and puts

them into a variable.

When using the INPUT statement, program

execution is suspended until a < cr> (Enter key) is

received. W hether this is a problem depends on

your particular application.

INPUT strips bit 7 on the COM1 port. This means

ASCII characters from 0 to 127 are received. The

INPUT statement can return a maximum string

length of 150 character s.

2. INKEY$(n) function. Characters are removed one

at a time. A null string is returned when the buffer

is empty.

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 25 26

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