Lp 922 Display Board (4008 S) - Fresenius Medical Care 4008 E Technical Manual

8.30 P.C.B. LP 922 Display board (4008 S)
8.30.1 Description
4008 E 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 25, either X1/24 (write) or X1/25 (read) is at L level. IC 20 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 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 33, the remaining keys on the touch
sensitive keyboard are connected to a matrix at the keyboard encoder IC 27 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 36.
Fresenius Medical Care 4008 4/09.03 (TM)
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