Fluke 900 - Manual (Page 15)

FLUKE 900 SERVICE MANUAL Theory of Operation
2.3 Micro Board
The Micro Board architecture is shown in the accompanying diagram. Note that, for
simplification, bus buffers are not shown and all chip select signals are shown as CS to a device
instead of the actual signal ( eg. CS for MAP CIO is actually MAPSEL ). The Z80 CPU runs at 6
MHz and operates with the Wait State Generator PAL (U69) to give the delayed control signals
WRD and RDD. The CPU signals WR and RD are thus modified for the timing requirements of
the Display Controller and the 8536 CIO chips. The four CIO devices are complex counterAimer
and parallel I/O ports. Two are located on the MB, two on the HSB, and they interrupt the CPU
for servicing of their particular function.
The MAP CIO sets up the memory map and paging scheme through PALs U58, U59, U72, U73.
Port A is configured as output for the PAL chip selects. Port B is output for the EPROM chip
selects. Port C is output for the RAM chip selects. The internal timer on this CIO is used for
general timeout purposes in such functions as cartridge operations and library loading.
The Decode Logic consists of the PALs referred to previously and it generates chip selects for all
peripheral devices and extends the 64K address range of the Z80 as shown in the memory mt^
diagram.
The first 16K is the power on
boot
ROM space (ROM
SYSAF is part of it). The
next 8K of CPU address
space is used to access 14
pages of 8K in size residing
on the SYSAF and B ROMs.
The next 8K starting at
address 6(X)0 accesses 14
pages residing on SYSC and
D ROMs. The range 8000 to
COOO is 16K of static RAM.
The first RAM chip has a
battery
and retains the
System Mode option
parameters. It also has 8
pages of cartridge memory
and
16 pages of library
ROM. The final 16 K is
overlayed
with 4 pages
comprising the DRAM and
used for internal functions
and
48K of ":SYST"
sequences.
The Keyboard CIO outputs levels on port A which are read back on port B when a key is
depressed. Three internal timers designated "watchdog", "key_time" and "key" take care of
4000
6000
8000
AOOO
COOO
FFFF
16k
SYSAF
8 k
OVERLAY
Ci;234S6iS9ABCiQ
8 k
OVERLAY
C i:24436789A8GD
8 k
SRAM
8 k
SRAM
1 5 k
DRAM
14 pages SYSAF
14 pages SYSB
14 pages SYSC
I N : i M M :; M pages SYSD
i|234S67aT234367a3ABGDEF
g
j 15 pages library
23
4 pages rSYST
2-3