Agilent Technologies ESA-E E4401B, Справочник пользователя/программиста

Страница: 195 / 426

Chapter 3 195
Programming Fundamentals
Overview of RS-232 (Option 1AX)
Pr
o
g
ram
m
ing
Fun
dam
e
nta
ls
Modem Line Handshaking
To use modem line handshaking for data transfer you would consider the following
tasks:
1. Set Data Terminal Ready and Request-to-Send modem lines to active state.
2. Check Data Set Ready and Clear-to-Send modem lines to be sure they are
active.
3. Send information to the interface and thence to the peripheral.
4. After data transfer is complete, clear Data Terminal Ready and
Request-to-Send signals.
For ENTER operations:
1. Set Data Terminal Ready line to active state. Leave Request-to-Send inactive.
2. Check Data Set Ready and Data Carrier Detect modem lines to be sure they are
active.
3. Input information from the interface as it is received from the peripheral.
4. After the input operation is complete, clear the Data Terminal Ready signal.
Data Transfer Errors
The serial interface can generate several types of errors when certain conditions are
encountered while receiving data from the peripheral device. Errors can be
generated by any of the following conditions:
• Parity error. The parity bit on an incoming character does not match the parity
expected by the receiver. This condition is most commonly caused by line
noise.
• Framing error. Start and stop bits do not match the timing expectations of the
receiver. This can occur when line noise causes the receiver to miss the start bit
or obscures the stop bits.
• Overrun error. Incoming data buffer overrun caused a loss of one or more data
characters. This is usually caused when data is received by the interface, but no
ENTER statement has been activated to input the information.
• Break received. A BREAK was sent to the interface by the peripheral device.
The desktop computer program must be able to properly interpret the meaning
of a break and take appropriate action.