Inside the Type 146 Unit Cha
ter Three: Overview
76
The Binary Coded Decimal (BCD) Board
The BCD board has an unwired, 25-pin female Type “D” connector. This board provides
input/output signals for hot cathode gauges.
The first four signals listed are inputs. The active low for the inputs requires about a 1 mA sink,
0.8 Volts maximum. The data inputs are read every 100 ms and require the recognition of a
transition. A minimum pulse width of 100 ms must be observed for the inputs to be activated.
The remaining signals are outputs. The open collector is tied to +5 Volts with 5.6K ohms. Data
changes after the falling edge of a strobe, and is valid on the strobe’s rising edge. The strobe
pulse is approximately 5 microseconds, and the BCD data is updated at a rate of 100 ms.
BCD Connector Pinout
Pin Number Assignment
3
Remote Off
4
Remote Degas
16 Reserved
17 Reserved
18 Least significant digit 1
19 Least significant digit 2
6 Least significant digit 4
5 Least significant digit 8
20 Most significant digit 1
21 Most significant digit 2
8 Most significant digit 4
7 Most significant digit 8
22 Exponent digit 1
23 Exponent digit 2
10 Exponent digit 4
9 Exponent digit 8
11 Exponent digit 10
24 Strobe
25 Status
Table 31: BCD Board Pinout
(Continued on next page)
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