Fluke Biomedical 945A - Manual (Page 57)

The outputs of U5 drive the latch enable pins on U50-U59 in pairs as shown in Table 4-16. U50-U59 are
BCD-to-7 segment latch/decoder/drivers. Each drives five segments (either red or green) with the
exception of U54 and U59 which drive four segments each. BCD to bargraph decoding is accomplished
by latching data into the appropriate device to turn on the required bargraph segments. Segment
decoding is shown below:
Typical 7 - Segment BCD Character
a
b
c
d
e
f
g
LED 1 OF 5 =
LED 2 OF 5 =
LED 3 OF 5 =
LED 4 OF 5 =
LED 5 OF 5 =
NONE = 1
7
3
9
8
A = F
Assume that all bargraph segments are off. Example: Write hex data 38 to bargraph address 4020. Data
38 is stored, low byte (8) in U55 and high byte (3) in U56. Data (8) in U55 causes the code for an 8 to be
output, which drives all output segments. The result is that the first five green LEDs turn on. Data (3) in
U56 causes the code for a 3 to drive segments 1,2, and 3 connected to that device. The result is that the
first 3 of 5 segments associated with U56 will turn on green.
Status Indicators (Write Only)
The status register (U60) is an 8 bit register with clear, and responds to address 4000. Data written into
U60 remains at the outputs until a reset occurs or new data is written. Upon initial power-up, the system
reset signal sets all outputs low. The status indicator write functions are listed in Table 4-17.
Table 4-17. Status Indicator Write Functions
Data Bit Function
D0 Check Source Indicator
D1 Rate-of-Rise (when applicable)
D2 Overrange Indicator
D3 Warn Indicator
D4 High Alarm Indicator
D5 R/hr Backlight
D6 KR/h Backlight
D7 mR/h Backlight
U60 output's, when high, control U61 inverter/driver to activate the appropriate front panel status
indicators. U60 output's, when low, control U61 to deactivate the appropriate front panel status
indicators.
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