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Null Message; Typical Procedure Example - NEC V321-2 Communications Manual

V321-2 : rs232 codes for v321, v421, v461
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Bit 5-2
Bit 1
Bit 0
H Freq: Horizontal Frequency in unit 0.01kHz
V Freq: Vertical Frequency in unit 0.01Hz
Ex.) When H Freq is '1''2''A''9' (31h, 32h, 41h, 39h), it means 47.77kHz.

5.5.3 NULL Message

Command code
The NULL message returned from the monitor is used in the following cases;
A timeout error has occurred. (The default timeout is 10sec.)
The monitor receives an unsupported message type.
The monitor detects a packet BCC (Block Check Code) error.
To tell the controller that the monitor does not have any answer to give to the host (not
ready or not expected)
Complete "NULL Message" command packet as follows;
SOH-'0'-'0'-'A'-'A'-'0'-'4'-STX-'B'-'E'-ETX-CHK- CR

6. Typical procedure example

The following is a sample of procedures to control the monitor, these are examples of "Get parameter",
"Set parameter" and "Save current settings".
6.1. How to change the "Brightness" setting.
Step 1. The controller requests the Monitor to reply with the current brightness setting and capability
to support this operation. (Get parameter)
SOH-'0'-Monitor ID-'0'-'C'-'0'-'6'
SOH (01h): Start Of Header
'0' (30h): Reserved
Monitor ID: Specify the Monitor ID from which you want to get a value.
Ex.) If Monitor ID is '1', specify 'A'.
'0' (30h): Message sender is the controller.
'C' (43h): Message type is "Get parameter command".
'0'-'6' (30h, 36h): Message length is 6 bytes.
STX (02h): Start of Message
'0'-'0' (30h, 30h): Operation code page number is 0.
'1'-'0' (31h, 30h): Operation code is 10h (in the OP code page 0).
ETX (03h): End of Message
Check code
BCC: Block Check Code
Refer to the section 4.5 "Check code" for a BCC calculation.
Reserved (Don't care)
1:Positive Horizontal sync polarity.
0:Negative Horizontal sync polarity.
1:Positive Vertical sync polarity.
0:Negative Vertical sync polarity.
Check code

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