Mallinckrodt NELLCOR NPB-4000, Service Manual

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Section 13: Microprocessor Computer and Control –Theory of Operation
13-19
Figure 13-13: Interface Timing
13.12 DUART Control
See Figure 13-14. The DUART is a Startech ST16C2550CJ44 which consists of
2 UARTs and fifos for the read and write portions of each UART. Channel 0 is
assigned to the RS-232 port, which exits the unit near the AC and DC inputs.
Channel 1 is assigned to the recorder. The fifos are 16 bytes deep, and transfer
to/from the DUART would save time if done on 8- or 16-byte boundaries.
Interfacing to the DUART is done by assigning CS4# to the DUART I/O space,
with four addresses assigned to each UART. The DUART channel 0 is the base
address assigned to CS4# and the channel 1 address is the base a 8 (A3).
There are four addresses assigned to each UART, 0,1,2,and 3.
Software must program two wait states for CS4# and define them as a byte
device.
A state machine in the FPGA is used to generate the proper signals for
programming the unit.
Figure 13-14: DUART Control
13.13 KNOB INTERFACE CONTROL
The knob consists of a rotary knob with a push switch. The knob is rotated and
the cursor on the LCD display moves forward or backward, depending on which
way the knob is rotated. When the knob is pushed, it must be detected and
indicated to the 386EX.