76
4-3 CMD_NAK
Description: Negative acknowledgment of received packet
Packet Format
Length
Opcode Status Cause Checksum
0x04
0x4E
(‘N’)
Field Descriptions
Table 4-4 Field Descriptions
Field Name
Format
Size
Description
Length
Length of message (not
including checksum).
1 Byte
Length Field
Opcode
0x4E
1 Byte
Identifies the opcode type.
Status
Bit 0
:
Retransmit
Bit 1-6
:
Unused
Bit 7: Command source
1 Byte
Bit 0: Identifies the transmission status.
Bit 7
:
1, Command is from the host.
0, Command is from the scanner.
All unused bits must be set to 0.
Cause
Reason code
1 Byte
Identifies the reason the NAK occurred:
Bit 0
=
busy, the scanner is executing a
command.
Bit 1
=
(NAK_RESEND) Checksum failure.
Bit 2
=
(NAK_BAD_CONTEXT) Unexpected or
Unknown message
Bit 3
=
(NAK_DENIED)
Bit 4
=
Reserved
Bit 5
=
Reserved
Bit 6
=
(NAK_NO_PARA) the parameters
wishing to change do not exist
Bit 7
=
(NAK_OUT_OF_RANGE) the
parameters wishing to change exceed the
range
Checksum
2's complement sum of
message
contents
excluding checksum.
2 Bytes
Checksum of message.
This message is sent when the received packet fails the checksum verification or some error occurred
while handling the message. If the scanner received NAK within this time period, it sends the previous
message again. The scanner retries twice before declaring a transmit error. The engine only resends a
message twice. If the message is not sent successfully either time, the engine declares a transmit error
and issues transmit error beep.
When ACK/NAK handshaking is disabled, the CMD_NAK message will not be sent.
It is not necessary to respond to a valid ACK or NAK message.
For example:
Length Opcode Status
Cause
Checksum
0x04
0x4E
0x00
0x40 (the parameter wishing to change is not existed) 0xFF 0x6E
Table 4-5 describes NAK types supported by the scanner.
Table 4-5 Scanner-supported NAK types
NAK Type
Meaning
Receiver Action
NAK_RESEND
Checksum incorrect.
Ensure checksum is correct. Limit
number of resends. Send packet again
with resend bit set (with the retransmit
status bit set).
NAK_NO_PARA
the parameter wishing to
change is not existed
Do not send the same message again.
Developer should ensure the proper
message is sent.
NAK_OUT_OF_RANGE
the parameter wishing to
change exceeds the range
Содержание ES910
Страница 1: ...ES910 Embedded Laser Barcode Scanner User Manual Version ES910_UM_EN_V1 1 7 ...
Страница 2: ......
Страница 10: ...4 1 4 Decode zone Figure 1 2 High density series ...
Страница 11: ...5 Figure 1 3 Long range series ...
Страница 106: ...100 11 Configuration alphanumeric entry barcode To finish parameter setting please scan the bar code below ...