Service manual

EXTERNAL SERIAL CONTROL PROTOCOL
B-5
April 2001
Part No. 001-9800-203
There are conditions under which a Command or
Event message cannot be properly processed. In these
cases, all devices must do one of the following:
• If the destination address was broadcast or was not
the device’s address, ignore the message.
• If the frame is an Information frame, ignore the
message.
• If the frame is undefined or unsupported and the
destination is the subscriber unit, respond with a
NAK message containing the proper error code.
• If the frame is undefined or unsupported and the
destination is an external device, ignore the
message.
• If the frame is supported but processing it causes an
error, respond with a NAK message containing the
proper error code.
ACK MESSAGE
Function
: This opcode is used by the destination
device to signal the source device that the last trans-
mission has been received and processed.
Destination Address Action
: The last directed message
transmitted may be deleted from the transmit
buffer.
Origin
: Any device on the bus.
Format
:
Data: None
NAK MESSAGE
Function
: This opcode is used by the destination
device to signal the source device that the last
directed frame has been received and some type of
problem has occurred.
Destination Address Action
: The last directed message
transmitted may be re-sent if the retry flag is on. If
the retry flag is off, the message should be deleted
from the transmit buffer and not retried.
Origin
: Any device on bus
Format
:
Data
:
Retry:
0x0 The message should not be re-sent
0x1 The message may be re-sent
Error Code:
0x00 Message unsupported or undefined. See
Rx Error which follows.
0x01 Bad parameter format
0x02 Parameter out of range
0x03 Unknown/unprogrammed bank, system or
group
0x04 Feature disabled
0x05 Hardware failure detected
0x06 Power off denied
0x07 Table full
0x08 Table empty
0x09 Table entry not found
0x0a In wrong mode
Receive Error
This field is included only when the error code is
0x00. A zero value indicates an invalid opcode, and a
non-zero value indicates that a receiver character error
occurred and that the message was ignored.
B.2.6 PACKET COLLISION
This specification does not deal with packet colli-
sion recovery. In a multi-drop environment, the hard-
ware or low level software drivers must prevent or
detect collisions.
Opcode
8 bits
0x0f
Opcode Retry Error Code Rx Error
8 bits 1 bit 7 bits 8 bits
0x0e