Operation | 19
1/3 Rack Block Downconverters (Option 17)
DNB1-XTR, Rev.N, 8/14/2012
®
External Fault Con
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guration
•
From the LCD Contrast/External Fault Screen, press the left or right arrow key to highlight the EXT FLT
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eld.
•
Use the up and down arrow keys to scroll through the available options until the desired setting is displayed. The
selections are N/A for not available, NO for normally open and NC for normally closed.
•
Press “ENT” to set the selection.
SERIAL PORT DESCRIPTION
The unit is supplied with an RS485/422 remote interface port. Status is always available at the RS485/RS422 remote
port regardless of control mode. Selection of Remote or Local control mode is available at the front panel only. The unit
defaults to Remote control upon power-up. If the unit is left in Local control mode, after thirty minutes of inactivity the unit
will switch to Remote control mode.
The RS485/RS422 serial port can be set to RS485 for two-wire operation or RS422 for four-wire operation from the front
panel local interface. This port supports a multi-drop bus arrangement. The RS485/RS422 interface parameters such as
address, baud rate and parity can be set from the front panel. All transmissions on the RS485/RS422 port are multi-byte
sequences beginning with a header byte and ending with a trailer byte followed by a checksum byte. The transmitted
bytes are all ASCII printable characters in the range of 20H to 7EH. The RS485/RS422 monitor and control protocols are
described in detail later in this section of the manual.
All messages addressed to the RS485/RS422 port are acknowledged with a response message. The unit continually
monitors the RS485/RS422 port and will accept commands, addressed to it, even in Local mode. When in Local mode,
receipt of any SET commands (commands beginning with “$”) at the RS485/RS422 remote port will be ignored and the
unit will respond with an error code.
REMOTE MESSAGE PROTOCOL (RS485/RS422)
The data format is a 10-bit sequence for each character. If odd or even parity is selected the ten bits are 1 Start, 7 Data, 1
Parity, and 1 Stop bit. If the parity is set to none, the bits are 1 Start, 8 Data and 1 Stop bit.
If any character in a command message contains an error in parity, framing, overrun or the checksum is incorrect,
the command is ignored and no response is made. When odd or even parity is selected, all characters, including the
checksum character, are checked for parity. The response time from command to acknowledge is 100 ms. maximum.
RS485/RS422 SERIAL PORT MESSAGE FORMAT
The Serial Message Format is as follows:
HEADER - ADDRESS - COMMAND/ERROR CODE - PARAMETERS - TRAILER –
CHECKSUM
The Header byte is 123 decimal (7BH, ASCII character “{“).
The address may take on the values from 64 to 95 decimal (40H to 5FH, ASCII characters “@” to “_”).
Commands are three ASCII characters preceded by an ASCII “?” or “$.” Commands preceded by “?” are QUERY
commands and those preceded by “$” are SET commands. Query commands are used to examine system parameters
while SET commands are intended to modify system parameters. An Error Code may be returned as a reply to an
unacceptable command.
Parameters are all ASCII printable characters in the range of 20H to 7EH. Numeric parameters are sent MSD
fi
rst, LSD
last. Values which do not adhere to the command format, or are beyond the allowable range, will be rejected and cause
the unit to respond with an error code.
The Trailer byte is 125 decimal (7DH, ASCII character “}”).
The checksum byte is the sum modulo 95 of all message characters beginning with the header byte up to and including
the trailer byte. The value 32 is subtracted from each character value before taking the modulo 95 sum. The value 32 is
added to the
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nal sum to obtain the checksum value. All values are in decimal.
Checksum = MOD [(character value - 32), 95] + 32
