Motorola DSP56012 - Manual (Page 147)

Parallel Host Interface
Host Interface (HI)
MOTOROLA DSP56012 User’s Manual 4-67
uncertainties of pipelined interrupt processing. For this reason, the HV should not be
changed at the same time the HC bit is cleared. However, the HV can be changed
when the HC bit is set.
4.4.8.4.6 Coordinating Data Transfers
When using the HOREQ pin for handshaking, wait until HOREQ is asserted and
then start writing/reading data using HEN or the HACK pin.
When not using HOREQ for handshaking, poll the INIT bit in the ICR to make sure it
is cleared by the hardware (which means the INIT execution is completed). Then,
start writing/reading data.
If using neither HOREQ for handshaking, nor polling the INIT bit, wait at least 6T
after the deassertion of HEN that wrote the ICR, before writing/reading data. This
wait ensures that the INIT is completed, because it needs 3T for synchronization
(worst case) plus 3T for executing the INIT.
4.4.8.4.7 Unused Pins
All unused input pins should be terminated. Also, any pin that is temporarily not
driven by an output during reset, when reprogramming a port or pin, when a bus is
not driven, or at any other time, should be pulled up or down with a resistor. For
example, HEN is capable of reacting to a 2 ns noise spike when not terminated.
Allowing HACK to float can cause problems even though it is not needed in a circuit.