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STP2002QFP
Sun Microelectronics
Fast Ethernet, Parallel Port, SCSI (FEPS) - STP2002QFP
These two bits allow selection of one of four possible handshake protocols.
The following table summarizes the protocol definitions for transfers to the
parallel port from the peripheral device.
For all protocol selections,P_BSY (PP_BSY) will become active if one of
the following conditions occur: TheP_DMA_ON bit is reset indicating
DMA cannot proceed; or the
P_FIFO is unable to accept more data. Internally, P_BSY (PP_BSY) will
always be generated for these conditions. However, if theP_BSY (PP_BSY)
pin is not configured as an output, it will not be driven and the external inter-
face will not be able to detect the busy condition. In this case, data could be
lost. In all cases, if P_BSY (PP_BSY) is asserted it will have the following
timing characteristics:
Figure 5.
The transfer modes are shown and discussed in the following sections.
4.3.1.3.1 No Handshake: (BUSY_OP=0, ACK_OP=0)
No handshake signals are generated in this mode. If P_ACK (PP_ACK) is
configured as an output, it will remain low or inactive.P_BSY (PP_BSY) will
be generated as required to gate further transfers, but not as a handshake sig-
nal. The operation of the interface as defined assumes the bidirectional sense
of each signal has been configured as follows: DIR=1, DS_DSEL=1,
ACK_DSEL=X,BUSY_DSEL=1. If P_ACK (PP_ACK) is configured as
an output, it will remain low or inactive. The configuration of P_BSY
(PP_BSY) as an output is suggested to avoid potential data loss. Reference
the parallel port timing section for detailed timing requirements for this mode.
4.3.1.3.2 Handshake with ACK: (BUSY_OP=0, ACK_OP=1)
Data transfers are acknowledged using P_ACK (PP_ACK). The position of
P_ACK (PP_ACK) relative to the trailing edge of data strobe is set using
DSS. Note that in this mode, the actual positioning of P_ACK (PP_ACK) will
beDSS plus 3 to 4 SBus clocks, due to synchronization delays. The width of
P_ACK (PP_ACK) is set usingDSW. P_BSY (PP_BSY) will be generated
P_D_STRB
(I)
DSS
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1.WHen data strobe is detected, P_BSY will be generated within 3 SBus clocks, if required.
2.P_BSY hold time after data strobe is configurable via DSS.