
MFC2000 Multifunctional Peripheral Controller 2000
Hardware Description
17-2
Conexant
100723A
17.1.5 ECP Forward
Extended Capabilities Port (ECP) Mode provides an asynchronous, byte-wide, bi-directional channel. The data
can be received by DMA mode or CPU mode as described in the Compatibility Mode section. The ECP protocol
provides the Data and command cycles types in both forward and reverse directions. The MODE = 2 and 3 for the
forward mode with RLE . When MODE is set to 2, ECP mode hardware handshaking is enabled during forward
data transfers, without RLE support. When mode 2 is programmed, the PPI responds to a high to low transition on
STROBEn (HostClk), and automatically sets and clears the BUSY bit in the Parallel Port Interface Register and
the BUSY to handshake with the host.. MODE may be reprogrammed at any time, but if an ECP cycle is currently
in progress, it completes as normal.
17.1.6 ECP Reverse
After a successful Forward to Reverse phase switch, the ECP changes into the reverse phase in MODE = 6.
When the 1284 interface is idle, this is the desired mode of operation. This mode will allow the MFC2000 ASIC to
inform the host of incoming fax data. The ECP Reverse mode can operate under
CPU interrupt driven control
or
automated DMA control. In CPU control, the software writes the outgoing byte into the output buffer and then sets
ACKn low to send the data. After the host completes the data transfer, the ACKn is automatically set high and the
CPU is free to respond to any PPI interrupts that have been enabled or to initiate an additional data transfer if
needed. The handshake signals are INITn, PE, ACKn, AUTOFDn and BUSY.
17.1.7 The Non-standard Dribble Mode
The dribble mode was used for the slower PC before P1284 is standardized. Dribble mode is similar to ECP in
that the channel can be reversed without having to go through a negotiation phase to turn the channel around. It
sends two bits at a time on the nPeriphRequest and XFlag signals rather than using the PIO data bus. In this
respect, it is similar to nibble mode's data transfer phase in that it uses HostBusy and PtrClk to transfer each
portion of the data byte. The dribble mode can only operate under CPU interrupt-driven control (no DMA mode).
Note
: This is not an IEEE-1284 mode but is useful to support certain product interfaces created
prior to the IEEE-1284 specification.
17.2 Additional Features
17.2.1 Filter
A digital filter is provided for incoming host control and data signals. SLCTINn, STROBEn, AUTOFDn, and INITn
are provided with digital filter circuits which are collectively controlled by software. IF DFIL =0, then no digital
filtering is selected.
Note that synchronization plus digital filtering adds up to four CLK periods of delay before a level change at one of
the host inputs appears in the Parallel Port Control Register, and five periods of delay before an output responds
to an input (e.g., before BUSY responds to STROBEn).
Likewise, synchronization and digital filtering of STROBEn affect the point at which ippid[7-0] and AUTOFDn are
latched into the parallel Port Data Register. Without a DFIL=3, ippid[7-0] and AUTOFDn are sampled an the fourth
rising edge of CLK after STROBEn is sampled. With digital filtering, ippid7-0 and AUTOFDn are sampled on the
fifth rising edge of CLK after STROBEn is sampled.