Signal transition events (normative) Each signal transition diagram has numbers
corresponding to the events that cause the transitions. The following is
a list of those events.
Host sets extensibility request value on data bus: 00h for Nibble Mode, 01h
for Byte Mode, etc.
Host requests an IEEE 1284 mode transfer by setting IEEE 1284 Active(nSelectIn)
high and HostBusy(nAutoFd) low.
Peripheral indicates IEEE 1284 support by setting AckDataReq(PError),
Xflag(Select), and nDataAvail(nFault) high, and PtrClk(nAck) low.
Host sets HostClk(nStrobe) low to latch extensibility request value into
After waiting the minimum HostClk(nStrobe) pulse width, host sets
HostClk(nStrobe) and HostBusy(nAutoFd) high to acknowledge the support by
the peripheral of IEEE 1284 protocol.
Xflag(Select) is set to reflect the support by the peripheral of the requested
extension. Busy is set to indicate whether the peripheral can accept data
from the host in the Compatibility Mode. For the Nibble and Byte Modes, the
peripheral sets nDataAvail(nFault) to indicate whether data is available
and AckDataReq(PError) to match nDataAvail(nFault).
Peripheral sets PtrClk(nAck) high, informing the host that the four interface
status signals are valid.
Host sets HostBusy(nAutoFd) low to indicate that it can accept data.
Peripheral places a nibble on the four status lines (low order nibble for
first handshake, high order nibble for second handshake).
Peripheral sets PtrClk(nAck) low to indicate that data is valid.
Host sets HostBusy(nAutoFd) high to handshake with the peripheral and (in
Nibble Mode) to indicate that it has received data and cannot accept more
at the moment.
Peripheral acknowledges receipt of data by the host by setting PtrClk(nAck)
Host sets HostBusy(nAutoFd) low, indicating that it can accept the second
Peripheral sets status lines to indicate if a subsequent peripheral to host
byte is ready to transfer, and sets PtrBusy to indicate its current forward
In Byte Mode, host places data bus in a high impedance state in anticipation
of peripheral-to-host transfer. In the Nibble Mode, the data bus is undefined.
In Byte Mode, peripheral places bytes on data bus.
Host sets HostClk(nStrobe) low. This event may happen after the falling or
rising edge of Ptr-Clk( nAck), i.e., events 9 and 11. It is defined in the
diagrams to occur coincident with event 10. The peripheral shall not interpret
this event as a latch signal for forward channel data.
Host sets HostClk(nStrobe) high. It shall occur before or coincident with
setting Host-Busy( nAutoFd) low (event 7).
Peripheral sets nDataAvail(nFault) low to indicate data is available, and
sets PtrClk(nAck) low.
After waiting the minimum pulse width, the peripheral sets PtrClk(nAck) high
to generate an interrupt to the host.
Host sets HostBusy(nAutoFd) high to acknowledge the request of the peripheral.
Peripheral sets AckDataReq(PError) low to acknowledge the host.
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