Symbol SE955 Integration Manual page 193

Table 10-5 describes NAK types supported by the SE955.
NAK Type
NAK_RESEND
NAK_DENIED
NAK_BAD_CONTEXT
The decoder only resends a message twice. If the message is not sent successfully either time, the decoder declares a transmit error
and issues transmit error beeps (LO-LO-LO-LO).
DECODE_DATA
Description: Decode data in SSI packet format
Packet Format
Length
Field Descriptions
Field Name
Length
Opcode
Message Source
Status
Bar Code Type
Decode Data
Checksum
The decoder uses this opcode when packeted data is selected to send decoded bar code data to the host. The decoded message is
contained in the Decode Data field.
Table 10-5. Decoder-Supported NAK Types
Meaning
Checksum incorrect.
Host is unable to comply with the
requested message (e.g., beep code is
out of range).
Host does not recognize the command.
Message
Opcode Source Status
0xF3 0x00
Format
Length of message (not
including checksum).
0xF3
0 = Decoder
Bit 0: Retransmit
Bits 1-7: unused
See Table 10-6
<data>
2's complement sum of
message contents excluding
checksum.
Receiver Action
Ensure checksum is correct. Limit number
of resends. Send packet again with resend
bit set.
Do not send data with this message again.
Developer should check values with
specified values. Developer should ensure
the proper character is sent, if using wake-
up character.
Bar code Decode
Type Data
Size Description
1 Byte Length Field
1 Byte Identifies this Opcode type.
1 Byte Identifies where the message is coming
from.
1 Byte Identifies the transmission status.
Unused bits must be set to 0.
1 Byte Identifies the scanned data code type.
Variable Data is decoded data including prefix and
suffix sent in ASCII format.
2 Bytes Checksum of message.
Simple Serial Interface 10-9
Checksum