8 module 8 - a, Nalog, Utput – Red Lion PAXT User Manual
Page 28: Arameters, Out asin, Type an-lo an-hi udt, Burn, Communication format, Parameter menu
28
Communication Format
Data is transferred from the meter through a serial communication channel.
In serial communications, the voltage is switched between a high and low level
at a predetermined rate (baud rate) using ASCII encoding. The receiving device
reads the voltage levels at the same intervals and then translates the switched
levels back to a character.
The voltage level conventions depend on the interface standard. The table
lists the voltage levels for each standard.
Data is transmitted one byte at a time with a variable idle period between
characters (0 to ∞). Each ASCII character is “framed” with a beginning start bit,
an optional error detection parity bit and one or more ending stop bits. The data
format and baud rate must match that of other equipment in order for
communication to take place. The figures list the data formats employed by
the meter.
Start bit and Data bits
Data transmission always begins with the start bit. The start bit signals the
receiving device to prepare for reception of data. One bit period later, the least
significant bit of the ASCII encoded character is transmitted, followed by the
remaining data bits. The receiving device then reads each bit position as they are
transmitted. Since the sending and receiving devices operate at the same
transmission speed (baud rate), the data is read without timing errors.
Parity bit
After the data bits, the parity bit is sent. The transmitter sets the parity bit to
a zero or a one, so that the total number of ones contained in the transmission
(including the parity bit) is either even or odd. This bit is used by the receiver
to detect errors that may occur to an odd number of bits in the transmission.
However, a single parity bit cannot detect errors that may occur to an even
number of bits. Given this limitation, the parity bit is often ignored by the
receiving device. The PAX meter ignores the parity bit of incoming data and
sets the parity bit to odd, even or none (mark parity) for outgoing data.
Stop bit
The last character transmitted is the stop bit. The stop bit provides a single bit
period pause to allow the receiver to prepare to re-synchronize to the start of a
new transmission (start bit of next byte). The receiver then continuously looks
for the occurrence of the start bit.
IDLE 0 b
0
1
b
2
b b
3
b
4
b
5
6
b
1 IDLE
IDLE
IDLE 0
b
b
0
b
1
3
2
b b
4
b
5
b
6
P 1
IDLE
IDLE 0
b
b b
0
1
b
b
3
2
4
b
b
5
6
1 1
(7 data, no parity, 2 stop)
(7 data, parity, 1 stop)
(8 data, no parity, 1 stop)
Start bit
Stop bit
Note: b - b is ASCII data.
0
7
7
b
Character Frame Figure
LOGIC
RS232*
RS485*
INTERFACE STATE
1
TXD,RXD; -3 to -15 V
a-b < -200 mV
mark (idle)
0
TXD,RXD; +3 to +15 V
a-b > +200 mV
space (active)
* Voltage levels at the Receiver
8-Out
ASIN
Analog
Type
tYPE
AN-LO
AN-HI
udt
Analog
Update Time
PAR
Analog
Assignment
Analog Low
Scale Value
Analog High
Scale Value
Pro
Burn-out
Action
burn
PAXT
ONLY
6.8 mOdUle 8 - a
nalOg
O
UTpUT
p
arameTers
(
) Ñ
PARAMETER MENU
Enter the analog output type. For 0-20 mA or 4-20 mA
use terminals 18 and 19. For 0-10 V use terminals 16 and
17. Only one range can be used at a time.
ANALOG TYPE
ANALOG ASSIGNMENT
SELECTION
0 to 10 V
4 to 20 mA
0 to 20 mA
RANGE
Enter the Display Value that corresponds to 0 mA (0-20
mA) , 4 mA (4-20 mA) or 0 VDC (0-10 VDC).
ANALOG LOW SCALE VALUE
ANALOG HIGH SCALE VALUE
ANALOG UPDATE TIME
PROBE BURN-OUT ACTION (PAXT ONLY)
to
to
to
Enter the source for the analog output to retransmit:
= Display Input Value
= Maximum Display Input Value
= Minimum Display Input Value
= Totalize Display Value
Enter the Display Value that corresponds to 20 mA (0-20
mA) , 20 mA (4-20 mA) or 10 VDC (0-10 VDC).
Enter the analog output update rate in seconds. A value
of 0.0 allows the meter to update the analog output at a
rate of 20/sec.
Enter the probe burn-out action. In the event of a
temperature probe failure, the analog output can be
programmed for low or high scale.
Ñ
- An analog output card must be installed in order to access this
module.