OKIDATA DOC-IT3000, Руководство по обслуживанию

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Service Guide DOC-IT3000/4000
Chapter 2 Principles of Operation
2.3.02 Doc-It Host Communication Controller
The Host Communications Controller (HCC) is an Oki proprietary ASIC which handles the
communications between the PC host and the i80960 processor. The key features are listed
below.
· Plastic quad flat pack-160 pins.
· Total power dissipation of 0.2W.
· Multiplexed address and data local bus, 16 or 32 bit width.
· Optional configuration EEPROM interface.
· System Time-out function.
· Local Bus memory read/write in i960 Burst Mode
The six major blocks of the HCC are discussed below.
AT Bus Interface
The AT Bus Interface block contains all of the signals which the Doc-It Controller board uses to
communicate with the PC-AT host. The signals enter/exit on the card edge connector of the
PC-AT. All signals with the exception of CLK14M (OSC) are routed through tri-state buffers or
transceivers. The CLK14M signal goes directly to the IPC chip through a damping resistor. These
signals (with the exception of the voltages and CLK14M) are then routed to the AT bus interface
block of the HCC. The signals used by the Doc-It Controller to communicate with the PC are as
follows.
BDATA 0-15 RESET REFRESH SBHE
IOCHRDY +5vdc, -12vdc, -12vdc IRQ7,10,12,14,15 LA17-23
AEN IOR, IOW BALE MEMR
SA0-16 MEMCS16 OSC MEMW
Besides acting as the interface block for the HCC chip, the AT interface contains the Time-Out
interrupt function for the board. In the case of a "lock-up" on the Doc-It Controller (when a memory
access from the host is not responded to within 2.5 microseconds) the Time-Out interrupt will
result and the PC host will be released immediately.
Local Bus Address Generator
This Doc-It Controller Local Bus block translates the PC-AT expanded and extended memory
addresses into the Local Bus memory address. There are two ways in which the HCC provides
PC access to the Doc-It Controller boards memory:
· Page Window
In this mode (which is normal mode of operation for DPS software), the HCC acts as a paged
DRAM controller for the PC host. The host can select any 16 Kbyte page of Doc-It Controller local
memory through Doc-It Controller Page Registers 0 and 1.
· Extended Memory
In this mode, the Doc-It Controller memory can be used as extended memory for the PC, much in
the same way that expansion memory cards provide additional memory to the system. In this