Table 41 - ECP Pin Descriptions
DESCRIPTION
NAME
nStrobe
TYPE
O
During write operations nStrobe registers data or address into the slave
on the asserting edge (handshakes with Busy).
PData 7:0
nAck
I/O
I
Contains address or data or RLE data.
Indicates valid data driven by the peripheral when asserted. This signal
handshakes with nAutoFd in reverse.
PeriphAck (Busy)
I
I
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.
PError
Used to acknowledge a change in the direction the transfer (asserted =
(nAckReverse)
forward).
nReverseRequest.
The peripheral drives this signal low to acknowledge
It is an "interlocked" handshake with
nReverseRequest. The host relies upon nAckReverse to determine
when it is permitted to drive the data bus.
Select
I
Indicates printer on line.
nAutoFd
O
Requests a byte of data from the peripheral when asserted,
(HostAck)
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.
nFault
(nPeriphRequest)
I
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.
nInit
O
O
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.
nSelectIn
Always deasserted in ECP mode.
97
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