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2.3.5. Serial Connection
The HVG-2020A has a 4-conductor TRRS 3.5 mm jack on the top of the instrument for digital communication.
To daisy chain instruments on a RS485 bus, Y-splitters of the 4-conductor variety are available. The HVG-2020A
can be configured to operate with either RS232 or RS485 signals via digital command or via the display.
Hastings uses a full duplex configuration. See the tables below for the standard pin-out.
COMMUNICATIONS CABLE PIN-OUT
Pin#
1 (Sleeve)
2 (Tip)
3 (Ring 1)
4 (Ring 2)
If making up a cable to interface from the TRRS 3.5 mm jack connector to a
standard PC 9-pin serial port (RS232), use the connections as listed here.
NOTICE: The serial cable length must be less than 30 meters long (unless housed
in a metal conduit) to meet CE Mark requirements.
The HVG-2020A uses RS485 receivers that are protected from bus over-voltages and will
not be damaged if connected to a bus without a driver or pull up resistors. The option to
enable 120-ohm termination resistors is available via the display or digital command.
They should be used if the instrument is the last one in a long cable length (prevents
miscommunications due to reflections). This is not normally necessary for short cables.
Do not have more than one instrument with these resistors enabled on any one cable run
as this will load down the cable. Hastings ships RS485 instruments without the resistors
enabled.
The default port set-up is 19.2K baud, 8 data bits, 1 stop bit, no parity and no flow control. A "carriage return"
signals the end of command input. The end of a response message from the HVG-2020A is signaled by a ">"
character. See Serial Communications section later in this manual for more information.
2.3.6. USB Connection
A USB micro-B connector is available that will implement a serial port interface. It will appear in the "Devices
and Printers" list as "Teledyne Hastings Digital" along with its assigned COM port number. The serial port
parameters are: 8 data bits, No Flow Control and 1 stop bit. The baud rate does not matter.
Only Windows 7 and 10 are supported. A device driver (THI_D300.inf) is needed for Windows 7, but not for
Windows 10.
2.3.7. TTL Serial Connection
TTL Serial output is available on the 9-pin D connector pins 7 (Tx out) and 9 (Rx in). The voltage levels are near
3.3 V for logic high and near 0 V for logic low. To communicate using a computer serial port, a TTL-to-serial
converter is required to raise the signal voltage levels to those required for RS232 communications.
HVG-2020A Instruction Manual
RS232
RS485
Common
TX+ (TDB)
TX
TX- (TDA)
RX
RX- (RDA)
NC
RX+ (RDB)
D9
TRRS
Female
NC
1
2
2
3
3
NC
4
1
5
NC
6
NC
7
NC
8
NC
9
Page 12 of 29
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