Functional Description - HP 340 Series Service Manual

Functional Description
The architecture of the card is straightforward. The SCSI Protocol Controller (or SPC) is
connected to the SCSI cable through single-ended line drivers. The other side of the SPC is
connected through a DIO-like interface. to the SPU.
A picture of the HP 98658A SCSI Interface Card is shown in Figure 3-13.
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Figure 3-13. HP 98658A SCSI Interface Card
Internal registers of the SPC are memory-mapped into the address space of the card, and appear
as 8-bit registers. These registers are readable at odd byte addresses. During writes, the proper
parity bit is always generated and supplied to the SPC. Any data written by the CPU in the
upper byte of a word transfer is ignored. A byte write to an even address will cause a bus error.
Parity generation is implemented for both the registers in the SPC and the DMA data path.
Parity checking is done by the SPC for the DMA path, and the result is available in the SERR
register. Due to the lack of parity on DIO, the actual parity bit cannot be transferred to or
from system RAM. Parity is odd when the parity configuration switch is set to 1.
Data words (16-bit) can be transferred under DMA control between the interface and main
system memory.
An interrupt circuit is available, and will normally be used to inform the host CPU of state
changes on the bus. The host initiates a transaction with the mass storage device, and then
responds to interrupts as it proceeds. The interrupt signal is generated by the SPC, and
logically ANDed with the IE bit from DIO register 3. Therefore, even the 'unmaskable' interrupt
described in the SPC manual can be inhibited.
An electronic fuse in the SCSl interface's +5 V dc power input will blow when excessive current
is drawn. When trying to boot an OS through the SCSI interface and the SCSI electronic fuse
blows, the fuse may be reset by re-starting the self-tests and boot sequence. Note that if the
condition that caused the fuse to blow has not been corrected, the fuse will blow again as soon
as the SPU is turned on.
If this fuse blows while HP-UX is executing, constant interrupts will occur. The SCSI driver
to turn off the SCSI interface. If the SCSI disc drive is a root disc in the HP-UX system,
that root disc drive will need to have its power cycled. However, if the root disc drive is used
with HP-IB, the HP-UX system will continue running but no SCSI discs will function until the
HP-UX system is taken down and power is cycled.
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Functional Description