reverse: Peripheral to Host communication
Pword: A port word; equal in size to the width
of the ISA interface. For this
implementation, PWord is always 8
bits.
EXTENDED CAPABILITIES PARALLEL PORT
ECP provides a number of advantages, some of
which are listed below. The individual features
are explained in greater detail in the remainder
of this section.
1
0
A high level.
A low level.
·
·
·
High performance half-duplex forward and
reverse channel
Interlocked handshake, for fast reliable
transfer
Optional single byte RLE compression for
improved throughput (64:1)
Channel addressing for low-cost peripherals
Maintains link and data layer separation
Permits the use of active output drivers
Permits the use of adaptive signal timing
Peer-to-peer capability
These terms may be considered synonymous:
·
·
·
·
·
·
·
·
·
·
PeriphClk, nAck
HostAck, nAutoFd
PeriphAck, Busy
nPeriphRequest, nFault
nReverseRequest, nInit
nAckReverse, PError
Xflag, Select
ECPMode, nSelectln
HostClk, nStrobe
·
·
·
·
·
Vocabulary
The following terms are used in this document:
Reference Document: IEEE 1284 Extended
Capabilities Port Protocol and ISA Interface
assert: When a signal asserts it transitions to a
"true" state, when a signal deasserts it
transitions to a "false" state.
Standard, Rev 1.14, July 14, 1993.
document is available from Microsoft.
This
forward: Host to Peripheral communication.
The bit map of the Extended Parallel Port
registers is:
D7
PD7
D6
D5
D4
D3
D2
D1
D0
Note
data
PD6
PD5
PD4
PD3
PD2
PD1
PD0
ecpAFifo
dsr
Addr/RLE
nBusy
0
Address or RLE field
2
1
1
2
2
2
nAck
0
PError
Select
ackIntEn
nFault
0
0
0
dcr
Direction
SelectIn
nInit
autofd
strobe
cFifo
ecpDFifo
tFifo
Parallel Port Data FIFO
ECP Data FIFO
Test FIFO
cnfgA
cnfgB
ecr
0
0
0
1
0
0
0
0
compress
intrValue
MODE
Parallel Port IRQ
nErrIntrEn
Parallel Port DMA
dmaEn
serviceIntr
full
empty
Note 1: These registers are available in all modes.
Note 2: All FIFOs use one common 16 byte FIFO.
Note 3: The ECP Parallel Port Config Reg B reflects the IRQ and DRQ selected by the
Configuration Registers.
89
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