90
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.
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
Vocabulary
The following terms are used in this document:
assert:
When a signal asserts it transitions to a
"true" state, when a signal deasserts it
transitions to a "false" state.
forward: Host to Peripheral communication.
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.
1
A high level.
0
A low level.
These terms may be considered synonymous:
PeriphClk, nAck
HostAck, nAutoFd
PeriphAck, Busy
nPeriphRequest, nFault
nReverseRequest, nInit
nAckReverse, PError
Xflag, Select
ECPMode, nSelectln
HostClk, nStrobe
Reference Document:
IEEE 1284 Extended
Capabilities Port Protocol and ISA Interface
Standard, Rev 1.14, July 14, 1993.
This
document is available from Microsoft.
The bit map of the Extended Parallel Port
registers is:
D7
D6
D5
D4
D3
D2
D1
D0
Note
data
PD7
PD6
PD5
PD4
PD3
PD2
PD1
PD0
ecpAFifo
Addr/RLE
Address or RLE field
2
dsr
nBusy
nAck
PError
Select
nFault
0
1
dcr
0
Direction
ackIntEn
SelectIn
nInit
autofd
strobe
1
cFifo
Parallel Port Data FIFO
2
ecpDFifo
ECP Data FIFO
2
tFifo
Test FIFO
2
cnfgA
0
1
0
cnfgB
compress
intrValue
Parallel Port IRQ
Parallel Port DMA
ecr
MODE
nErrIntrEn
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.