Fluke Biomedical 945A - Manual (Page 54)

PROM 8000 directly drives the enable pins of the PROM. RAM 0000, RAM 2000 and RAM Read are
logic OR'd with Clock from U17. RAM Read drives the RAM output. Enable pins RAM 0000 and RAM
2000 act as chip enables for the appropriate RAM. RAM Write is logic OR'd with Write 02 by U17, which
is connected to the write enable pins on the rams. The 5000 Block output signal is applied to driver U74
and connect to J3, the optional interface connector.
The I/O output signal is applied to major function decoder U1 which is a 1 of 8 decoder. U1 utilizes
address lines A5, A6, A7, and A8 as well as Clock to generate outputs which are decoded in 32 hex
blocks starting at address 4000. Table 4-12 lists U1 outputs, their functions and addresses.
Table 4-12. U1 Outputs
Address
State Address Function
A8 A7 A6 A5
0 0 0 0 4000 Register Select
0 0 0 1 4020 Bargraph
0 0 1 0 4040 ACIA (Communication Interface)
0 0 1 1 4060 SCA (Analyzer)
0 1 0 0 4080 GPIB (General Purpose Interface Bus)
0 1 0 1 40A0 (Spare)
0 1 1 0 40C0 (Spare)
0 1 1 1 40E0 (Spare)
Address 4000 is further decoded by the write register decoder (U2) and the read register decoder (U34).
The bargraph output, address 4020, is further decoded by U5. The remaining output address (4040
through 40E0) are provided to the optional interface connector for use by external option circuit boards.
PROM
The Programmable Read Only Memory is typically a 27256 which is a UV erasable 32K x 8 bit PROM.
U23, which responds to address 8000-FFF, is always present. U23 contains the operating program for
the UDR (firmware). Jumper JP2 is normally set from 2 - 3. By setting JP2 from 2 - 3, A14 is applied to
pin 27 of U23 which allows the use of a 27256 PROM (32K x 8).
RAM
Dynamic Random Access Memory (U21) is utilized for temporary data storage. U21 responds to address
0000-1FFF (8K x 8 bit). Data stored in the RAM is lost on power down since this data is not backed up
by battery power.
E2
Sixteen (16) monitor specific, operator entered setpoints are stored in 64 bytes of electrically erasable
memory (E2). U33 provides storage for the setpoints (256 bytes max.). The 16 setpoints are loaded
serially into RAM memory (U21) upon power up. U35 is an 8-Bit control register for the setpoints.
Setpoint values stored in the (E2) are retained during power-down.
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