Lp 649-2 Display Board (4008 B/S) - Fresenius Medical Care 4008 E Technical Manual

8.23 P.C.B. LP 649-2 Display board (4008 B/S)
8.23.1 Description
4008 B/S 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 X635/12 – 15 for IC 1 as well as X635/16 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)
Pin 1 and Pin 2 of connector 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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