Setting The Flow Control Option; Description - Racal Instruments 1256 Manual

Switching system

Table of Contents

1256 User Manual

Setting the Flow

Control Option

GPIB and RS-232 Interfaces 4-10

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Description

Flow control is a means by which the data terminal (or host

computer acting as a terminal) may pace the flow of data coming

from the 1256 so that the terminal has time to properly receive the

data. It also allows the 1256 to pace commands coming from the

terminal so that the 1256 has sufficient time to execute the

commands as they arrive.

The 1256 provides three flow control options:

•

XON/XOFF: Software flow control. The RS-232 device that is

receiving data may send an XOFF character (ASCII 19

sending device, commanding the sending device to suspend

data output. Later, when the receiving device is ready for more

data, it may send an XON character (ASCII 17

sending device, indicating that data transmission may be

resumed.

•

CTS/RTS: Hardware flow control. The 1256 normally holds

the RS-232 Clear-To-Send (CTS) line in the TRUE state (-12

volts). When the 1256 is receiving data, and needs to have

data transmission suspended, it takes the CTS line to the

FALSE state (+12 volts). When it is ready for more data, it

returns the CTS line to the TRUE state. Similarly, the data

terminal uses the RS-232 Request-To-Send (RTS) line to pace

data coming from the 1256. The data terminal normally holds

the RTS line in the TRUE (-12 volts) state. To suspend data

from the 1256, it takes the RTS signal to the FALSE state (+12

volts). To resume data transfer, the terminal takes the RTS

signal TRUE again.

•

Disabled: No flow control. If your terminal does not support

flow control, set the 1256 to disable flow control. Note that

sending large blocks of data without flow control may

necessitate a slower baud rate to avoid data overrun problems.