PSYNC | 29 | OUT |
This output line is provided to identify those cycles
in which the microprocessor is doing an OP CODE fetch.
The ?SYNC line goes high during PH1 of an OP CODE fetch
and stays high for the remainder of that cycle. If ABC
or DMA/ is low during the rising edge of PH1,in which
pulse PSYNC went high, the processor will stop in its
current state and will remain in the state until either
AEC or DMA/ goes high. In this manner, the SYNC signal
can be used to control either the AEC or DMA/ line to
cause single instruction execution. |
AEC | 30 | IN |
This input signal is the Address Enable Control line.
When high, the address bus, R/W are valid. When low,
the address bus, R/W and MAP/ are in a high-impedance
state except for A17, A18 and A19 each of which will
be connected to the A16 line. |
DMA/ | 31 | IN |
This signal is connected to a 3K passive pullup.
When this signal is low the address bus and R/W will
be tri-stated. This will allow external DMA devices
to assume control of the system bus lines. |
(READY) | Internal Signal |
This signal is generated internally via the AEC and
DMA/ lines. The READY signal goes high when both AEC
and DMA/ are high. It goes low if either ABC or DMA/
goes low. The READY signal allows the user to single-cycle
the microprocessor on all cycles including write
cycles. A low state on either DMA/ or AEC during the
rising transition of phase one (PHI) will deassert the
READY line and halt the microprocessor with the output
address lines holding the current address. This feature
allows micro processor interfacing with low speed
memory as well as fast (max 2 cycle) Direct Memory
Access (DMA). |
IO/ | 32 | IN |
This input signal is used to select the internal
registers of the device, provided memory is not being
mapped by the CPU.
|
MAP/ | 33 | OUT |
This signal is passively pulled-up (3 Kohm) whenever
DMA/ or AEC is pulled low. This output signal is used
to indicate whether or not-memory is being mapped by
the device. If the CPU is addressing a mapped memory
region the MAP/ line will go low and will inhibit the
10/ line from selecting an internal register If the
CPU is not mapping memory the MAP/ line will be high
and A16-A19 will be kept low.
|