Fluke Biomedical 945A - Manual (Page 55)

Read - Write Cycles
A read cycle is performed by sequencing RAM 0000 and RAM Read, while RAM Write is held high
(inactive). The address (A0 - A12) are latched by the failing edge of RAM 0000. Data becomes valid
approximately 250 ns later.
A write cycle is performed by sequencing RAM 000 and RAM Write, while holding RAM Read high
(inactive). Identical to the read cycle, the address (A0 - A12) are latched by the falling edge of RAM 000.
Data is strobed into RAM on the failing edge of RAM Write.
Write Register Decoding
Decoding for write registers within the main circuit board is performed by U2, which is a 1 of 8 decoder.
Control signals for U2 are Reg. Select, R/W (active high), Write 02 as well as addresses A1, A2, and A3.
U2 decodes two addresses per output, starting at 4000, and ending with 400E. These outputs are active
low. Table 4-13 lists write registers, their assigned function and address.
Table 4-13. Write Register Functions
Address State Hex Address Function
A3 A2 A1
0 0 0
4000 Status Indicators
0 0 1 4002 E2 PROM
0 1 0 4004 D/A Converter
0 1 1 4006 Display Control
1 0 0 4008 Display Data
1 0 1 400A Counter Control
1 1 0 400C Relay Control
1 1 1 400E (Spare )
Counter Control (Write Only)
The counter control register (U43) is an 8 bit register with clear, and responds to address 400A. Upon
initial power-up, the system resets all outputs low. Table 4-14 lists the counter control register write
functions.
NOTE
Data written into U43 remains at the outputs until a reset occurs or new data is
written.
Table 4-14. Counter Control Register Write Functions
Data Bit Function
D0 Counter Clear
D1 Counter Enable
D2 Not Used
D3 Not Used
D4 Clear Switch Latch
D5 Not Used
D6 Not Used
D7 Not Used
4-31