900240 Rev. B
3/01
page 9
3.5
Interface Pin Descriptions
The table below shows pin assignments for the 9-pin D-shell connector. Different pins are used to supply either regulated
5V
dc
or unregulated 6V to 15V power. Only one of the two power pins (9 or 8) should be connected in a given
installation.
Name
In/Out
Pin
Description
TxD / A
Out
2
RS-232 transmit out / RS-485 transmit-receive signal
RxD / B
In
3
RS-232 receive in / RS-485 transmit-receive return
GND
In
5
Power and signal common
6-15V
In
9
Unregulated power input
5V
In
8
Regulated power input
Oper / Calib *
In
1
Operate / Calibrate-* input (open = Operate)
Run / Stop *
In
6
Run / Stop- input (open = Run)
Ready / Sleep *
In
4
Ready / Sleep- input (open = Ready)
Cont / Reset *
In
7
Continue / Reset- input (open = Continue)
Table 3. Interface Signal Descriptions
*A dash following a signal name is used to denote that the signal is asserted active low.
In this case, when pin 1 is low the Calibrate function is selected.
3.6
Communication
The HMR3000 serial communications are governed by a simple, asynchronous, ASCII protocol modeled after the
NMEA 0183 standard. Either an RS-232 or an RS-485 electrical interface can be used. ASCII characters are transmitted
and received using 1 start bit, 8 data bits (LSB first), no parity (MSB always 0), and 1 stop bit ; 10 bits total per character.
Baud rate can be any one of 1200, 2400, 4800, 9600, 19200, 38400.
The HMR3000 supports both standard NMEA 0183 and proprietary messages. Unsolicited NMEA messages are sent by
the HMR3000 in Continuous Mode at the rates programmed in EEPROM. HMR3000 also responds to all input messages
from the host. An HMR3000 response to a command input may be delayed due to transmission of an unsolicited output.
The host must wait for HMR3000 to respond to the last command input before sending another command message.
All communication from and to HMR3000 contain a two-character Checksum Field at the end of the data fields, and are
denoted in the following sentences by ‘hh’. The checksum assures the accuracy of the message transmitted. This
checksum is calculated per NMEA 0183 Standard, and is outlined in section 3.11.
3.7
Input
There are two kinds of input to the HMR3000, request for output sentence, or a setting of a configuration parameter.
HMR3000 sends a response to all valid inputs with a correct checksum value.
1.
Response to a Request for output sentence is the appropriate sentence.
2.
Response to parameter input will be #!0000*21 to indicate the command and the parameter was accepted.
