Redpost RPC-80 - External Link Setup; External Link Socket; Serial Handshaking

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EXTERNAL LINK SETUP

This section covers the serial format settings and use of the External Link.

The External Link menu allows you to set the serial format for communications on

the link.

A series of menus lets you choose the:-

Baud Rate ( 300 to 19200 )

Number of Data Bits ( 7 or 8 )

Number of Stop Bits ( 1 or 2 )

Parity ( None, Odd or Even )

Handshake (Hard or Soft)

All these must be set up to match the serial format of the external computer

connected to the external link.

The final menu in this series lets you select the type of serial handshaking as either

HARD HANDSHAKE RTS/CTS or SOFT HANDSHAKE XON/XOFF. These terms are

explained in more detail below under the sub-heading "Serial Handshaking". The

handshaking must be chosen to match that of the external computer connected to

the external link.

External Link socket

The External Link socket is a female 25 way "D" connector arranged in the RS232

Data Terminal Equipment (DTE) format. The connections are:-

Signal Name in/out notes

1 Chassis ground

2 Transmit Data (TXD) out

3 Receive Data (RXD) in

4 Request to Send (RTS) out hard handshake

5 Clear to Send (CTS) in hard handshake

7 Signal ground

14 (test signal) out fixed "Off" (-9 volts)

20 Terminal Ready (DTR) out fixed "On" (+9 volts)

Serial handshaking

When serial communications take place between two parties there may be times

when either party is temporarily unable to receive data. In order to prevent data from

being lost the communication is controlled by a handshake system that signals to

each party when the other party is ready and able to receive.

Hard Handshake

In the Hard Handshake system the handshaking is managed by two extra signal

connections. The signals are described below from the point of view of the RPC-80.

Clear to Send (CTS) is an input to the RPC-80 that controls the transmitter in the

RPC-80. The signal comes from the RTS or DTR output of the external computer.

When CTS is On the RPC-80 will transmit its data, when CTS is Off the RPC-80 will

wait and not transmit.