
The external bus interface
UM0404
DocID13284 Rev 2
Figure 63. Memory cycle time
8.3.3
Programmable memory tri-state time
The ST10F276 allows the user to adjust the time between two subsequent external
accesses to address slow external devices. The tri-state time MTTC starts when the external
device has released the bus after deactivation of the read command (RD).
The output of the next address on the external bus can be delayed for a memory or
peripheral which needs more time to switch off its bus drivers, by introducing a wait-state
after the previous bus cycle (see
During this memory tri-state time wait-state, the CPU is not idle, so CPU operations will only
be slowed down if a subsequent external instruction or data fetch operation is required
during the next instruction cycle.
The memory tri-state time wait-state requires one CPU clock and is controlled via the
MTTCx bit of the BUSCON registers. A wait-state will be inserted, if bit MTTCx is ‘0’ (default
after reset).
External bus cycles in multiplexed bus modes implicitly add one tri-state time wait-state in
addition to the programmable MTTC wait-state.
Any MTTC wait-states are applicable to both read and write cycles.
Data/Instr.
MCTC Wait States (1...15)
Bus Cycle
Segment
ALE
BUS (P0)
RD
BUS (P0)
WR
Address
Address
Address
Data