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STP2002QFP
Sun Microelectronics
Fast Ethernet, Parallel Port, SCSI (FEPS) - STP2002QFP
DS:
Reading this bit reflects the state of the bidirectional PP_STB pin. Writing
this bit with DS_DSEL=0 or with DS_SEL=1 and DIR=0 will cause the value
written to be driven onto PP_STB. The reset state of the output latch is 0, but
the value read back from this bit after reset will reflect the input signal being
driven onto PP_STB.
ACK:
Reading this bit reflects the state of the bidirectional PP_ACK pin. Writing
this bit with ACK_DSEL=1 will cause the value written to be driven onto
PP_ACK if DIR=1. The reset state of the output latch is 0, but the value read
back from this bit after reset will reflect the input signal being driven onto
PP_ACK.
BUSY:
Reading this bit reflects the state of the bidirectional PP_BSY pin. Writing
this bit with BUSY_DSEL=1 will cause the value written to be driven onto
PP_BSY if DIR=1. The reset state of the output latch is 0, but the value read
back from this bit after reset will reflect the input signal being driven onto
PP_BSY.
DIR:
This bit defines and controls the direction of data transfer: 0=write to external
device,
1= read from external device. It is also driven externally on the PP_DDIR pin.
This bit also controls the direction of DMA operation. In the case of a mem-
ory clear operation, this bit (must be set) and the MEM_CLR bits define the
Table 34: Transfer Control Register Deļ¬nition
Field Bits Description Type
DS 0 Data strobe R/W
ACK 1 Acknowledge R/W
BUSY 2 Busy (active low) R/W
DIR 3 Direction control. 0 = write to external device, 1 = read R/W
4 Unused (reads as 0) R
5 Unused (reads as 0) R
6 Unused (reads as 0) R
7 Unused (reads as 0) R