to be repeated. Decompression simply intercepts the RLE byte and repeats the following byte the specified number of
times. Hardware support for compression is optional.
SMSC DS – LPC47M192
Page 90
Rev. 03/30/05
DATASHEET
Table 41 – ECP Pin Descriptions
NAME
TYPE
O
DESCRIPTION
nStrobe
During write operations nStrobe registers data or address into the slave
on the asserting edge (handshakes with Busy).
Contains address or data or RLE data.
Indicates valid data driven by the peripheral when asserted. This signal
handshakes with nAutoFd in reverse.
This signal deasserts to indicate that the peripheral can accept data. This
signal handshakes with nStrobe in the forward direction. In the reverse
direction this signal indicates whether the data lines contain ECP
command information or data. The peripheral uses this signal to flow
control in the forward direction. It is an “interlocked” handshake with
nStrobe. PeriphAck also provides command information in the reverse
direction.
Used to acknowledge a change in the direction the transfer (asserted =
forward). The peripheral drives this signal low to acknowledge
nReverseRequest.
It
is
an
nReverseRequest. The host relies upon nAckReverse to determine when
it is permitted to drive the data bus.
Indicates printer on line.
Requests a byte of data from the peripheral when asserted, handshaking
with nAck in the reverse direction. In the forward direction this signal
indicates whether the data lines contain ECP address or data. The host
drives this signal to flow control in the reverse direction. It is an
“interlocked” handshake with nAck. HostAck also provides command
information in the forward phase.
Generates an error interrupt when asserted. This signal provides a
mechanism for peer-to-peer communication. This signal is valid only in
the forward direction. During ECP Mode the peripheral is permitted (but
not required) to drive this pin low to request a reverse transfer. The
request is merely a “hint” to the host; the host has ultimate control over
the transfer direction. This signal would be typically used to generate an
interrupt to the host CPU.
Sets the transfer direction (asserted = reverse, deasserted = forward).
This pin is driven low to place the channel in the reverse direction. The
peripheral is only allowed to drive the bi-directional data bus while in
ECP Mode and HostAck is low and nSelectIn is high.
Always deasserted in ECP mode.
PData 7:0
nAck
I/O
I
PeriphAck (Busy)
I
PError
(nAckReverse)
I
“interlocked”
handshake
with
Select
nAutoFd
(HostAck)
I
O
nFault
(nPeriphRequest)
I
nInit
O
nSelectIn
O
Register Definitions
The register definitions are based on the standard IBM addresses for LPT. All of the standard printer ports are
supported. The additional registers attach to an upper bit decode of the standard LPT port definition to avoid conflict
with standard ISA devices. The port is equivalent to a generic parallel port interface and may be operated in that
mode. The port registers vary depending on the mode field in the ecr. The table below lists these dependencies.
Operation of the devices in modes other that those specified is undefined.
Table 42 - ECP Register Definitions
NAME
data
ecpAFifo
dsr
dcr
cFifo
ecpDFifo
tFifo
cnfgA
cnfgB
ecr
ADDRESS (Note 1)
+000h R/W
+000h R/W
+001h R/W
+002h R/W
+400h R/W
+400h R/W
+400h R/W
+400h R
+401h R/W
+402h R/W
ECP MODES
000-001
011
All
All
010
011
110
111
111
All
FUNCTION
Data Register
ECP FIFO (Address)
Status Register
Control Register
Parallel Port Data FIFO
ECP FIFO (DATA)
Test FIFO
Configuration Register A
Configuration Register B
Extended Control Register