P.c.b. Lp 635 Display Board; Description - Fresenius Medical Care 4008 E Technical Manual

8.15

P.C.B. LP 635 Display board

8.15.1

Description

4008 E hemodialysis machine – monitor
Address decoder (circuit diagram 1/7)
IC 1 and IC 2 are provided as 4-in-16-bit address decoders. The 22 chip selects are generated by
means of addresses A0 to A3 and A4 for IC 1 as well as A4 inverted for IC 2. The 22 chip selects
are generated only if, via IC 9, either X635/24 (write) or X635/25 (read) is at L level. IC 71 is used
as data bus driver and is reversed in its direction by WR and RD.
Keyboard matrix (circuit diagram 5/7)
Pins N1 and GND of plug X2 are directly connected to the circuits in the power supply unit. These
circuits are used to switch the machine on and off. Via IC 54, the remaining keys on the touch
sensitive keyboard are connected to a matrix at the keyboard encoder IC 53 and an additional
data line DB4. After the CPU has received the interrupt, the keyboard code is read out by means
of CS20 via buffer IC 73.
Brightness control (circuit diagram 1+2/7)
The clock pulses required for the bar graph displays are delivered by IC 74 and the following gate
logic. Superimposed by a higher frequency and a variable mark-to-space ratio, these clock
pulses are used to modulate the brightness. To this end, the shift register IC 6 is provided. IC 6 is
loaded in parallel with the desired mark-to-space ratio via a data word at DB0 to DB7 (CS21) and
is cyclically rotating due to clock generator IC 7/11, 12, 13, and IC 7/8, 9, 10.
Status indicator LEDs (circuit diagram 6/7)
All status indicators as well as the condition indicator are switched by means of IC 21 and IC 25
(CS16, CS17).
Both modules are
– connected to the brightness control by R1,
– not connected to the brightness control by R2 (maximum brightness).
The I/O LED (power on/off) is directly connected to the 5-V supply network.
Alarm indicator LEDs (circuit diagram 7/7)
All alarm indicators are energized by IC 23 and CS18. The key click is controlled by output 19 of
IC 23 via IC 46/5.14.
Fresenius Medical Care 4008 4/09.03 (TM)
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