
MFC2000 Multifunctional Peripheral Controller 2000
Hardware Description
17-22
Conexant
100723A
17.6 Firmware Operation
All the Parallel Port negotiations will be done in firmware.
17.6.1 Disabling All Hardware Handshaking
When hardware handshaking is disabled(MODE=0), software is then responsible for controlling the parallel port
interface. Software can control all parallel port operations including negotiation and termination phases, as well as
reverse channel transfers. This provides flexibility to adapt to existing protocols as they are revised and to new
protocols as they are created.
Software can control the BUSY and ACKn interface pins with the FBSY (force BUSY) and FACK (force ACKn)
bits in the Parallel Port Interface Register. The FBSY bit is OR’ed with the BUSY output from the PPI state
machine before driving the BUSY interface pin, and the FACK bit is NOR’ed with the ACKn output from the PPI
state machine before driving the ACKn interface pin. Normally the PPI state machine should be idle when using
FBSY and FACK. Even with all hardware handshaking disabled, the Parallel port register continues to latch
parallel port data on the leading edge of the STROBEn. Software can issue a RST in the Parallel Port Control
Register to immediately force the PPI state machine to idle.
17.6.2 Software Interrupts
The following is a list of P1284 signal transition interrupts provided for ease of use:
SLCTINn
STROBEn
INITn
AUTOFDn
DRX
CRX
IVT
RDX
HTE
Rising and Falling
Rising and Falling (remains high until data is fetched from PPI)
Rising and Falling
Rising and Falling
Data Received
Command Received
Invalid Transition
Reverse Data Transmitted
Host Time-out Error
17.6.3 Interrupt Operation
There will be a bit corresponding to each interrupt in the interrupt enable register that enables the interrupt. When
the event corresponding to an interrupt occurs, this bit needs to be set at the following rising edge of the SIU
clock. The PPI Interface possesses 15 sources of interrupts. Each source can post an event in the interrupt status
register and each event can be individually enabled or disabled in the interrupt mask register. The fifteen
interrupts have been in Section 17. The first eight interrupt events signal level changes that occur at the host
control signal input pins. Note that these events are detected after the host inputs are synchronized, digitally
filtered, and recorded in the parallel Port Interface Register.