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Model 3585A
Circuit Functional Descriptions
6·25. PROCESSOR DESCRIPTION (Service Group C)
The Processor section of the -hp- 3585A is best understood through the use of a block
diagram. The IDA bus (Instruction, Data and Address Bus) carries communication between
the Central Processor (A41), the ROM (A43) and the RAM (A42). The memory control bus
carries the handshake control protocol, choosing ROM or RAM, indicating that RAM is
busy being refreshed, etc. The IOD Bus
(110
Data Bus) carries data from the Central Pro
cessor to the
110
(A45) interface board, to the HP-IB (SG F) board, and to the Counter (SG
G) board. An
110
control bus and an I/O status bus conduct the same function with the
110
board as does the memory control bus with the Central Processor and memory.
The ROM size is 16k by 16, while the RAM size is 4k by 16. Direct Memory Access (DMA)
exists between the display processor and RAM. The Display Processor pulls the DMA line
low , causing the Central Processor to address RAM and transfer the required information
through the central processor, through the I/O interface and to the Display Processor much
faster than would normally be possible (the entire process takes about 2.5 usec). The A/D
interrupts the Central Processor and gives it information every 200 usec (5000
times/second).
One final note of general information, most of the buses in this section are Low
=
True.
A41 is the Central Processor board. The block diagram shows what is included on this
board. The processor chip is identical to the chip used in the -hp- 9825 Desktop Computer.
You will also notice that the "beeper" is located on the A41 board.
The A42 board contains the RAM and its associated circuitry, including refresh circuitry.
The A43 board contains ROM and its suport circuitry.
The A45 is the
110
board. This board contains the tri-state buses, decoders, latches, and
gate and timing circuitry necessary for directing data to various
110
sections . Finally, A47 is
the keyboard. An 8 by 9 matrix system is used to monitor the front panel keys. The rest of
this board is LED's and their drive circuitry and the RPG (Rotary Pulse Generator) cir
cuitry.
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Summary of Contents for 3585A
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