Lp 924 Display Board (4008 H) - Fresenius Medical Care 4008 E Technical Manual

8.32 P.C.B. LP 924 Display board (4008 H)
8.32.1 Description
4008 H hemodialysis machine – monitor
Address decoder (circuit diagram 1/6)
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 3, either X1/24 (write) or X1/25 (read) is at L level. IC 7 is used as data
bus driver and is reversed in its direction by WR and RD.
Keyboard matrix (circuit diagram 1/6)
Pins N1 and GND of plug X3 are directly connected to the circuits in the power supply unit. These
circuits are used to switch the machine on and off. Via IC 14, the remaining keys on the touch
sensitive keyboard are connected to a matrix at the keyboard encoder IC 12 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 13.
Brightness control (circuit diagram 1+2/6)
The clock pulses required for the bar graph displays are delivered by IC 10 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 5/4,5,6 and IC 5/8,9,10.
Fresenius Medical Care 4008 4/09.03 (TM)
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