Grass Valley 2200 - Manual (Page 22)

2-8
Section 2 Ð Editor Protocol
Error Detection
Transmission Errors
Error detection is a normal part of the communication process. For this Protocol
Interface, error detection and reporting is limited to problems that occur at the
transmission and reception level of communication. These type of errors fall into
two basic categories, line and time-out errors.
Line errors include three speciÞc types of errors that may occur with each
character transmission and reception.
¥ Parity error
¥ Framing error
¥ Data Overrun error
These errors occur when the Serial Data Word becomes corrupted.
Time-out errors occur when too much time elapses between the reception of
characters during a message transmission.
When the Editor Interface detects communication errors, it responds with a
negative acknowledge of 85H and then aborts all communications. Any remaining
un-executed commands are discarded after the error indication occurs and the
Interface is forced back into the Idle state. Refer to Figure 2-2 on page 2-2 and Table
2-1 for details of the detection and corresponding response to each error type.
In order to resume communications, the Editor must transmit a break/address
sequence to return the channel to the Select state. If the Editor Interface does not
receive a valid tributary or poll address following the break, it falls back into the
Idle state without transmitting the 85H Negative Acknowledge byte. Line errors
that occur during an attempt to send and receive the address byte still result in a
Negative Acknowledge byte being sent back to the Editor.