Mindeo FS580, Руководство пользователя

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77
5-3 CMD_ACK
Description: Positive acknowledgment of received packet.
Packet Format
Length Opcode Status Checksum
0x03 0x59
Field Descriptions
Field name Format Size Description
Length 0x03 1 Byte Length of Field
Opcode 0x59 1 Byte Identifies the command being sent.
Status
Bit 0: Identifies transmit status
Bit 6-1: Unused
Bit 7: Command source
1 Byte
Bit 0:
0=First time packet is sent
1= Subsequent transmission attempts
Bit 7:
0=Command is from the scanner
1=Command is from the host
All unused bits recommend to be set to 0.
Checksum
2’s complement sum of message
contents excluding checksum
2 Bytes Checksum of message
CMD_ACK message is sent to the SCI packet transmitter when the received packet passes the
checksum check and no negative acknowledgment conditions apply. If the data to be sent is in response
to a command (e.g. REQUEST_REVISION), CMD_ACK message is not in need.
ACK/NAK handshaking can be disabled, but this is not recommended.
It is not necessary to respond to a valid ACK or NAK message.
For example: Scanner sends ACK.
Length Opcode Status Checksum
0x03 0x59 0x00 0xFF 0xA4
Host Requirements
The host must send a CMD_ACK or response data within the programmable Response delay to
acknowledge receipt of all messages, unless noted otherwise in the message description section.
Scanner Requirements
If the scanner does not receive an ACK within Response delay, it sends the previous message again.
The scanner retries twice more (with the retransmit status bit set) before declaring a transmit error.