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HDR-40 HDR-50 RS-422 Protocol Reference V1.0
1. Interface Overview
Conforming to EIA RS-422A.
Full duplex communications channel is utilized.
Data is transmitted asynchronously, bit serial, word serial with data exchange between devices.
Standard transmission rate on the interface bus is 38400 bits per seconds (bps)
The data word utilized by the interface system is as follows :
1 Start bit + 8 Data bits + 1 Parity bit + 1 Stop bit. Odd Parity
ODD parity: The total of “1”s in D0+D1+ . . . D7+PARITY equals an odd number.
2. Command Block Format
The data communication is composed of the
CMD-1/DATA COUNT
byte, the
CMD-2
byte, optional
DATA
bytes and the
CHECKSUM
byte. Commands are transmitted in order from the MSB (Most Significant Byte)
to the LSB (Least Significant Byte). This means that when using the examples in this manual, the order in
which the bytes are read is the same order in which they are transmitted. When the
DATA COUNT
nibble is
0, no
DATA
bytes are transmitted or required (the
CMD-1/DATA COUNT
byte,
CMD-2
byte and
CHECKSUM
byte are still transmitted). When the
DATA COUNT
nibble is not 0, the number of
DATA
bytes transmitted
must correspond with the
DATA COUNT
. These bytes are inserted between the
CMD-2
byte and
CHECKSUM
byte.
COMMAND BLOCK FORMAT
The data communication between the controller and the device is performed as follows:
Name
CMD-1 Data
Count
CMD-2 Data
0~15
(per Data Count)
Checksum
Nibble MSN LSN
Size
1 Byte
1 Byte
0..15 Byte(s)
1 Byte
1. MSN stands for Most Significant Nibble (4 bits)
2. LSN stands for Least Significant Nibble (4 bits)
COMMAND CONTENTS
CMD-1
:
This is the first (Most Significant) nibble of the first byte of the command. The DATA COUNT (below)
fills the lower (Least Significant) nibble. It indicates the command or return group to which the command
belongs as per the table below
CMD-1 Function
Initiator
0x System
Control
Controller
1x
System Control Return
Device (HDR UNIT)
2x Transport
Control
Controller
4x
Preset And Select Control
Controller
6x Sense
Request
Controller
7x
Sense Return
Device (HDR UNIT)
Ex DVR
Control
Controller
Fx
DVR Return
Device (HDR UNIT)
DATA COUNT
:
This is the second (Least Significant) nibble of the first byte of the command. The upper (Most Significant)
nibble is filled by the
CMD-1
(above). It indicates the number of data bytes (0-15) that are required to be
inserted between the
CMD-2
byte and the
CHECKSUM
byte.
D0
D1 D2 D3 D4
D5
D6
D7
PARITY
(ODD)
START
BIT
STOP
BIT
USO
RESTRITO
