BCD Interface Signals
Chapter Three: Overview
34
BCD Connector Pinout for Type 270-5 (5½ digit display) (Continued)
Pin Number
Description
Pin Number
Description
43
Chan 1 ID
47
Decimal -2P
44
D1P
48
Decimal -1P
45
Decimal 0P
49
+5 Volt Return
46
Decimal -3P
50
Chan 2 ID
* Used only by MKS
Table 10: BCD Connector Pinout for the Type 270-5 (5½ digit display)
BCD Interface Signals
The 270 instrument can communicate over the
REMOTE DISPLAY HOLD
, Data Ready, and
Enable lines on the BCD connector.
REMOTE DISPLAY HOLD Line
This line enables remote display control of the 270 instrument. Left open, the display will
update at a rate of 2.5 samples per second. Holding this line low prohibits any updates to the
display. To command the display to update, generate a positive going pulse with a duration of
50 microseconds, minimum, to 2 milliseconds, maximum.
Data Ready Line
This line goes high when the data is valid and ready to read.
Enable Lines
The BCD information is controlled by the enable lines. The 4½ digit 270-4, has six enable lines
while the 5½ digit 270-5, has only one. (The displayless unit does not have any enable lines.)
When these lines are connected to ground, all of the BCD information is at the connector and is
valid when the DATA READY line goes high. When these lines are left open, or connected to
+5 V, all of the BCD outputs are open. This is done when several meters are connected in
parallel to a common bus. Each meter is strobed for a reading by grounding these control lines,
and then when the reading has been taken, the lines are forced high again and the outputs are
open.
Note
The channel ID and decimal point information is not controlled by these
enable lines. This data is active at all times.
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