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6. ALLOCATION OF BUFFER MEMORIES (BFM)
6.1 Buffer memories
BFM
*#0
Characteristic change
CH1 to CH4 Averaged temperature reading to be
*# 1 - #4
averaged (1 to 256) Default = 8
#5 - #8
CH1 to CH4 Averaged temperature in 0.1°C units
#9 - #12
CH1 to CH4 Present temperature in 0.1°C units
#13 - #16
CH1 to CH4 Averaged temperature in 0.1°F units
#17 - #20
CH1 to CH4 Present temperature in 0.1°F units
#21 - #27
Reserved
*#28
Digital range error latch
#29
Error status
#30
Identification code K2040
#31
Reserved
1) BFM #0 value (K0 or K1) decides the Pt100 characteristic to be used.
K0 : JIS C 1604-1997
K1 : JIS C 1604-1981
2) The number of samples to be averaged are assigned in BFMs #1 to #4. Only the range 1 to 4096 is
valid. Values outside this range are ignored. The default value of 8 is used.
3) A number of recently converted readings are averaged to give a smoother read out. The averaged
data is stored in BFMs #5 to #8 and #13 to #16.
4) BFMs #9 to #12 and #17 to #20 store the current value of the input data. This value is in units of 0.1°C
or 0.1°F, but the resolution is only 0.2°C to 0.3°C or 0.36°F to 0.54°F.
6.2 Status Information
1) Buffer Memory BFM #28: Digital range error latch
BFM #29 b10(digital range error) is used to judge whether the measured temperature is within the
unit's range or not.
BFM #28 latches the error status of each channel.
b15 or b8
Not used
Low : Latches ON when the temperature measurement data drops below the lowest
temperature measurement limit.
High : Turns ON when the temperature measurement data rises above the highest
temperature measurement limit.
When an error occurs the temperature data before the error is latched. If the measured value returns
to within valid limits the temperature data returns to normal operation. (Note: The error remains
latched in (BFM #28))
An error can be cleared by writing K0 to BFM #28 using the TO instruction or turning off the power.
2) Buffer Memory BFM #29: Error status
Bit devices of BFM #29
b0 : Error
b1 : Reserved
b2 : Power source
b3 : Hardware error
b4 to b9 : Reserved
b10 : Digital range error
b11 : Averaging error
b12 to b15 : Reserved
3) Buffer Memory BFM #30: Identification Code
The identification code or ID number for this Special Block is read from buffer memory BFM #30 using
the FROM instruction. This number for the FX
The PLC can use this facility in its program to identify the special block before commencing data
transfer from and to the special block.
CONTENTS
b7
b6
High
Low
CH4
When either b2 or b3 is ON
A/D conversion is stopped for
the error channel.
Reserved
24V DC power supply failure.
A/D converter or other
hardware failure.
Reserved
Digital output/analog input
value is outside the specified
range.
Selected number of averaged
results is outside the available
range -see BFM #1 to #4
Reserved
b5
b4
High
Low
CH3
ON
-4AD-PT unit is K2040.
2N
The FX
-4AD-PT communicates
2N
with the PLC via buffer memories.
BFMs (buffer memories) #21 to #27
and #31 are reserved.
All BFM data can be read by the
PLC using the FROM instruction.
P L C c a n r e a d / w r it e t h e B F M s
(marked with "*" ), using FROM /TO
instructions.
b3
b2
High
Low
CH2
OFF
No error
Reserved
Power supply normal
Hardware Normal
Reserved
Digital output value is normal.
Averaging is normal.
(between 1 to 4096)
Reserved
b1
b0
High
Low
CH1
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