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SIMPLE SERIAL INTERFACE
61
4.2 SSI MESSAGE FORMATS
The following sections describe each of the SSI messages that can be
communicated between the reader and host. See
required to transmit these messages.
CMD_ACK
Description: Positive acknowledgment of received packet
Packet Format
Length
Opcode
Message
Source
Status
Data
Checksum
0x04
0XD0
Field Descriptions
Field Name
Format
Size
Description
Length
Length of message
(not including
checksum).
1 Byte
Length Field
Opcode
0xD0
1 Byte
Identifies this opcode type.
Message Source
0 = Reader
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.
Data
None
Checksum
2's complement
sum of message
contents excluding
checksum.
2 Byte
Checksum of message.
This message is sent to the SSI packet transmitter when the received packet passes
the checksum check and no negative acknowledgment conditions apply (see
CMD_NACK).
Note
:ACK/NACK handshaking can be disabled, but this is not recommended. It is not
necessary to respond to a valid ACK or NACK message.
Содержание Dragon D151
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