Hamilton Sundstrand Company Fuel Metering Valves XVG - Manual (Page 4)

1 Serial Communication
The primary interface used for XVG/eXVG is serial communication, which is the
exchange of data one-bit-at-a time, sequentially, on a single data line or channel.
XVG/eXVG can communicate either in PECC (a propriety standard protocol) or
Modbus protocol via the serial interface.
2 Baud Rate
Baud rate is the speed at which a data line changes its state or the number of times per
second the line changes state. If two serial devices are connected together via direct
cables, then baud rate and bit-per-second are the same. XVG/eXVG Modbus
communication supports baud rates of 9600, 19200, 38400, and 57600.
3 Parity bit
A parity bit is optionally transmitted along with data to help detect data corruption
that may occur during transmission. There are three parity modes available: Odd,
Even, or None. XVG/eXVG Modbus communication default parity setting is Even.
4 Start and Stop Bits
The start bit informs the receiving device that a character is coming; a stop bit
indicates that a character is completed. The start bit is always 0 and stop bit is always
1. Per Modbus protocol requirements, XVG/eXVG Modbus communication employs
1 stop bit in Even or Odd parity mode, and 2 stop bits in None parity mode.
5 Electrical Interface Standards
XVG/eXVG serial communication uses either RS232 for one-to-one connection or
RS485 for a multi-drop capable network.
- RS232 interface uses three wires: transmit, receive, and common (ground) line.
A -3 to -12V signal indicates a 1, a +3 to +12V signal indicates a 0.
Communication is one-to-one, and full-duplex capable. Distance is limited to
50 feet.
- RS485 interface uses two wires: T+/R+ and T-/R-. The RS485 receiver
compares the voltage difference between both lines instead of the absolute
voltage level on a signal line.
Communication is half-duplex and up to 32
devices can be connected to a multi-drop network up. Distance is limited to
4000 feet.
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