Modem Line Handshaking; Data Transfer Errors - HP ESA-E Series Programmer's Manual

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.
Chapter 1
Programming Fundamentals
Overview of RS-232
1-13