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DPP Hardware Component Replacement Guide DPP001 and up
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SCSI circuit pack (NT6M66xx) - Turbo
only
General description
The Small Computer System Interface (SCSI) Interface circuit pack, in slot
11 of the A and B chassis of a Turbo DPP system, is a smart circuit assembly
with its own 64180 microprocessor, EPROM, local RAM, and dual-ported
RAM. It is considered a peripheral of the microprocessor on the main CPU
(A1).
The SCSI circuit pack is the link to the disk drive. It transfers data from and
to the bus used for recording on or reading from the disk. The stored program
on the SCSI circuit pack provides read and write commands to the disk drive.
This circuit pack performs a SCSI Host Adapter function and resembles an
Initiator of Priority 7 to the SCSI bus. Target operation is not provided due to
the complexity of an external Y type crossover network which supports
redundant storage elements. 32 Kbytes of DPR are used as interface and
control for commands and data to and from the Main CP at slot 1. The SCSI
circuit pack provides the following capabilities:
• Interface to implement 380-Mbyte disk drives with the 56K polling
feature; must be equipped when 760-Mbyte, 1-Gigabyte and 2-Gigabyte
disk drives are used.
• Interface between DPP system backplane and SCSI hard disk drives.
• 32 KBytes of parity protected DPR for command and data passing to and
from the Main CPU at slot 1.
• Fully transparent DPR implementation allowing virtually simultaneous
access from either port without using wait states.
• Host port of DPR (Main CPU side; slot 1) designed to support fully
asynchronous access based on 4 mHz timing of standard Z80 bus cycle
without WAIT states.
• 6 MHz processor clock with DPR synchronized and running alternate half
clock cycles. (Host cycles occur during the first half of every T state
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