Symbol SE 923, Integration Manual

Page: 177 / 238

6-21
Simple Serial Interface
PARAM_REQUEST
Description: Request values of selected parameters
Packet Format
Field Descriptions
The host uses this message to request selected parameters from the decoder.
Host Requirements
The host requests the decoder’s current values for specific parameters by listing the parameter
numbers in the Request_Data field. If the host asks for a parameter value not supported by
the decoder, the decoder does not send a value for this unsupported param_num. If none of
the requested values is supported, an empty PARAM_SEND message is transmitted. If the
host requests the value of all the parameters, it sends a special param_num called
ALL_PARAMS (0xFE) in the first position of the Request_Data field.
Note: The decoder’s response to this command is PARAM_SEND, not
ACK. Depending on the time-out set, and the number of parameters
Length Opcode Message Source Status Request Data Checksum
0xC7 0x04
Field Name Format Size Description
Length Length of message (not
including checksum). 1 Byte Length Field
Opcode 0xC7 1 Byte Identifies this Opcode type.
Message
Source 4 = Host 1 Byte Identifies where the message is
coming from.
Status Bit 0: Retransmit
Bit 1-7: Unused 1 Byte Identifies the transmission status.
Unused bits must be set to 0.
Request Data <Param_num><Param_num>
<Param_num>... Variable
Checksum 2's complement sum of message
contents excluding checksum. 2 Bytes Checksum of message.