4-6
4.14 TRANSMISSION VOLTAGE LEVELS
The voltage levels accepted by the meter are those of the standards, and the meter
outputs are well regulated and well within the standards. The two wires carrying the
signal are designated “A” and “B”; for RS-232, “B” is taken as the 0 V ground.
Table 4.2. Meter Receiving Voltages
“1” BIT/MARK “0” BIT/SPACE
OPTION TYPE OR STOP BIT OR START BIT
RS-232 –3 > A > –15 V +3 < A < +15 V
RS-422 or 485 A < (B–0.2 V) A > (B+0.2 V)
Table 4.3. Meter Transmitting Voltages
“1” BIT/MARK “0” BIT/SPACE
OPTION TYPE OR STOP BIT OR START BIT
RS-232 –6 > A > –7 V +6 < A < +7 V
RS-422 or 485 A < (B–2 V) A > (B+2 V)
The RS-422/485 transmissions from the meter are 3-state, and both receive and
transmit are zener-protected.
4.15 RECOGNITION CHARACTER
A selectable symbol (e.g., the asterisk, *) transmitted as the first character of each
message from the computer, which is used for message security: the meter ignores
messages without this symbol.
4.16 RAM
The acronym for “Random Access Memory”. For the meter, the storage for the data
and instructions for the immediately-occurring operation. When given a “RESET1” or
“soft” reset, the meter restarts its operation from the data in RAM. “PUT” commands
insert information from the computer into RAM, and “GET” commands transmit RAM
information to the computer.
4.17 EEPROM
The acronym for “Electrically Erasable Programmable Read-Only Memory”. For the
meter, the non-volatile memory for the setup and configuration data is retained
independent of power or resets. Upon a “RESET2” or “hard” reset (e.g., after any
BLOCK WRITE command), the data in the EEPROM is copied into RAM, discarding
whatever data had been running. “WRITE” commands insert information from the
computer into EEPROM, and “READ” commands transmit EEPROM data to the
computer.
4. Definitions
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