Fluke Biomedical 960CD-220 - Manual (Page 15)

Theory of Operation
Bus Interface Logic
2
2-1
Section 2
Theory of Operation
2.1 Bus Interface Logic
Refer to Drawing 960CD-220-13, sheet 1 in Appendix B. Bus Interface signals are buffered and
distributed internally on the module and externally on the data bus. The internal address buffers, Z16 and
27 are permanently enabled. The external address bus is buffered by two bi-directional IC’s Z15 and Z28.
Z14 provides internal data bus buffering of D0 to D7. It also inverts the internal data signal. IR/W (internal
read/write) controls the direction of data flow. The external data bus is buffered by Z26, an inverting
buffer.
2.2 Address Decoding Circuitry
Refer to Drawing 960CD-220-13, Sheet 2 in Appendix B. Z29 is a programmable array logic (PAL) with
four sets of inputs; address bits A8 through A15, IR/W, VMA, and SHORT 02. Z29 is programmed as
shown in Table 4-1.
Memory consists of Z38, a 32K x 8-bit EPROM, and three 8K x 8 bit static RAMs (Z39, Z40, and Z41).
Table 2-1. Address Decoding Circuitry Programs
Title Program Hex Address Function
DISPID /A8*A9*/A10*/A11*/A12*/A13*/A14*/A15*VMA 200-2FF
Display or channel ID
addressed
ACIA1 A8*A9*/A10*/A11*/A12*/A13*/A14*/A15*VMA 300-3FF
Communications
channel 1 addressed
ACIA2 /A8*/A9*A10*/A11*/A12*/A13*/A14*/A15*VMA 400-4FF
Communications
channel 2 addressed
ACIA3 A8*/A9*A10*/A11*/A12*/A13*/A14*/A15*VMA 500-5FF
Communications
channel 3 addressed
BKSL
/A8*A9*A10*/A11*/A12*/A13*/A14*/A15*VMA*
SHORT02*IRW
600-6FF
Bank selected memory
addressed
DS /A9*/A10*/A11*/A12*/A13*/A14*/A15*VMA 000-1 FF External device address
PROM /A15*VMA 8000-8FFF
32K PROM in Z38
addressed
RAM3 A13*A14*/A15*VMA 6000-7FFF
Memory in Z41
addressed
RAM 1 A13*/A14*/A15*VMA 2000-3FFF
8K RAM in Z39
addressed
RAM2 A13*A14*/A15*VMA 4000-5FFF
8K RAM in Z40
addressed
Battery backup for RAM memory is provided with a lithium iodide battery. This battery has a useful life
expectancy in excess of ten years. However, care should be taken when handling the controller module. If
placed on a conductive surface, the battery could be shorted out. The lithium iodide battery, B1, requires
no periodic maintenance. It is a primary cell battery that cannot be recharged.