Z53C80SCSI ZILOG [Zilog, Inc.], Z53C80SCSI Datasheet - Page 15

• Manufacturer Part Number: Z53C80SCSI
• Description: SMALL COMPUTER SYSTEM INTERFACE (SCSI)
• Manufacturer: ZILOG [Zilog, Inc.]

D7
D7
Parity Error. An interrupt is generated for a received parity
error it the Enable Parity Check (bit 5) and the Enable Parity
Interrupt (bit 4) bits are set (1) in the Mode Register. Parity
is checked during a read of the Current SCSI Data Register
and during a DMA receive operation. A parity error can be
detected without generating an interrupt by disabling the
Enable Parity Interrupt bit and checking the Parity Error
flag (Bus and Status Register, bit 5).
The proper values for the Bus and Status Register and the
Current SCSI Bus Status Register are displayed in Figures
21 and 22, respectively.
PS97SCC0200
Z
ILOG
X
0
Figure 20. Current SCSI Bus Status Register
X
X
X
0
Figure 19. Bus and Status Register
X
1
X
X
X
0
X
X
X
X
D0
D0
/ACK
/ATN
Busy Error
Phase Match
Interrupt Request Active
Parity Error
DMA Request
End of DMA
/DBP
/SEL
I//O
C//D
/MSG
/REQ
/BSY
/RST
D7
D7
Bus Phase Mismatch. The SCSI phase lines have the
signals I//O, C//D, and /MSG. These signals are compared
with the corresponding bits in the Target Command
Register: Assert I//O (bit 0), Assert C//D (bit 1), and Assert
/MSG (bit 2). The comparison occurs continually and is
reflected in the Phase Match bit (bit 3) of the Bus and Status
Register. If the DMA Mode bit (Mode Register, bit 1) is
active and a phase mismatch occurs when /REQ transitions
from False to True, an interrupt (IRQ) is generated.
0
0
Figure 22. Current SCSI Bus Status Register
X
1
1
1
Figure 21. Bus and Status Register
X
1
X
1
X
0
X
0
X
X
D0
D0
/ACK
/ATN
Busy Error
Phase Match
Interrupt Request Active
Parity Error
DMA Request
End of DMA
/DBP
/SEL
I//O
C//D
/MSQ
/REQ
/BSY
/RST
Z53C80 SCSI
15