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STP2002QFP
Fast Ethernet, Parallel Port, SCSI (FEPS) - STP2002QFP
Sun Microsystems,
4.3.1.4 Master Read/Write Protocol (Xerox Mode)
This section describes the parallel port operation while master read cycles are
performed. Operation while master write cycles are performed is the same as
is described in the “Unidirectional Operation (Transfers to the Peripheral De-
vice)” section on page 15.
Data transfer for master read cycles is accomplished by the master gener-
ating a data strobe (request for data) with no data present on the P_DATA
(PP_DATA) bus. The peripheral responds by placing data on the P_DATA
(PP_DATA) bus and generating an P_ACK (PP_ACK) which functions as a
strobe. Only one handshake protocol is valid for master read cycles and is
described below.
4.3.1.4.1 Handshake with ACK: (BUSY_OP=0, ACK_OP=1)
Data is transferred to the HIOD by the use of P_ACK (PP_ACK).
P_D_STRB (PP_STB) width is defined by DSW. DSS is used to define the
required interval from P_ACK (PP_ACK) to the next P_D_STRB (PP_STB).
P_BSY (PP_BSY) will gate further data transfers if present. The operation of
the interface as defined assumes the bidirectional sense of each signal has
been configured as follows: DIR=1,DS_DSEL =0,ACK_DSEL =0,
BUSY_DSEL=0. Reference the data transfer diagram in Figure 9.
Figure 9.
4.3.2 Programmed I/O ModeProgrammed I/O mode is intended to allow the parallel port to operate prima-
rily under software control. Data latching, interrupt, and busy generation are
performed in hardware as required. The following two sections describe op-
DSS
DSW
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3
1.Data strobe width as defined in the hardware configuration register.
2.DSS is used for ACK to P_D_STRB stiming (Hardware configuration register).
3.Acknowledge is used as a strobe and is required for each byte transferred.
4.If P_BSY is active, it gates further data transfers.
5.All signal polarities shown are at the HIOD pins. Polarities on the interface cable should be inverted (except P_DATA).
P_DATA (I)
P_D_STRB
(O)
P_ACK (I)
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