Fluke Biomedical 945A - Manual (Page 53)

Data Transceivers
Data transceiver U16 is an octal tri-state bi-directional transceiver which provides drive capability to the
data bus. The MPU data I/O signals are connected to U16 "A" ports. U16 "B" ports drive the data bus
under control of the read/write signal. When U16-11 is low, data is transferred from the "B" ports (internal
bus) to the "A" ports (MPU data). When U16-11 is high, data is transferred from the "A" ports (MPU data)
to the "B" ports (internal bus) during a write cycle.
Data transceiver U73 provides buffer and drive capability to the external data bus interface, available for
optional circuit boards on J3. Data direction is controlled by the read/write line on U73-11 providing U73-
9 (bus enable) is low, which enables port to port data transfer to occur. The bus enable signal is
generated by the option board/boards when they are addressed by the MPU. When U73-11 is low, for a
read cycle, data is transferred from the external bus to the internal bus. When U73-11 is high, for a write
cycle, data is transferred from the internal bus to the external bus.
Control Signal Buffer
Line driver U18 provides a signal drive for all system control signals and clocks utilized by circuitry within
the main circuit board.
Line driver U74 provides the drive for control lines and clock signals for external circuitry utilizing the J3
option interface connector.
Address Decoding
The master decoder (U14) is an open-collector 32 x 8 bit bipolar PROM. Address lines A15, A14, A13,
and A12 as well as read/write are used to decode memory and I/O addresses in 4K hex blocks. Table 4-
11 lists the output signals from U14.
Table 4-11. Output Signals (U14)
U14 Pin
Signal Name Address Read/Write
9 PROM 8000 8000-FFFF Read Only
7
Spare Spare
6 RAM 2000 (future) 2000-3FFF Read/Write
5 RAM 0000 0000-1FFF Read/Write
4 I / O 4000-4FFF Read/Write
3 RAM Write 0000-3FFF Write Only
2 RAM Read 0000-3FFF Read Only
1 5000 Block 5000-5FFF Read/Write
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