Datavideo DN-400, Инструкция по эксплуатации

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RS 422 Command Set / Protocol Version 1.2
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 second (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.
RS 422 Version History
Date: 2010/10/20 Version: 1.2
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.
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 1 Byte
MSN stands for Most Significant Nibble (4 bits) and LSN stands for Least Significant Nibble (4 bits)
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 (
CMD-1)
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 (DN-400)
2x Transport Control Controller
4x Preset And Select Control Controller
6x Sense Request Controller
7x Sense Return Device (DN-400)
Ex DVR Control Controller
Fx DVR Return Device (DN-400)
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