RCA COSMAC Operator's Manual page 60

INTERFACING SIGNALS (cont'd)
Some users may want to design and breadboard control
electronics to interface directly to the 40-pin COS~~C
CPU. These users should pick up the appropriate sig-
nals as follows:
signal slot pin
DUSO-N to BUS7-N 18
M
to
V
MREAD-N 18 20
CLEAR-N, L¢AD-N, TPA-Nl, TPB-Nl 21 10,A,2,l
EFl-N to EF4-N 21 3 to 6
DMAIN-N, DMA¢UT-N, INTERRUPT-N 21 9,7,8
SCO-N. SCl-N
17
11,12
NQ~N
to N3-N
17
18 to 15
The COS~'1AC Microprocessor t-1anual (pages SO through 60)
has several examples of designing input/output logic which
interfaces directly with the 40-pin COSMAC CPU. That
manual, supplemented by the data sheet for the COSMAC CPU,
includes sufficient information to guide the user in such
an endeavor. The signal naming convention in the COSMAC
Microprocessor Manual differs slightly from that adopted
here. A low assertion signal is indicated by an overline,
~.e., TrA.
This is equivalent to the TPA-N notation in
this manual. Similarly MWR there is equivalent to MWR-P
here.
Timing for DMA requests and INTERRUPTS are shown in the
COSMAC Microprocessor Manual. As explained there, any DMA
request or INTERRUPT will cause the COSMAC CPU to make a
transition out of the IDLE state (repetitive Sl's), and
cause program execution to commence. The COSMAC CPU is
sensitive to both DMA and INTERRUPT after RESET because CLEAR
puts it into an IDLE state. Thus CLEAR (both CLEAR-N and
CLEAR-P are available) should be used to disable these ex-
ternal requests until they are required. User devices should
not issue DMA or INTERRUPT requests until explicitly per-
mitted by program or by logic.
To complete this section, the implementation of DMA channels
and INTERRUPT logic, in the Microkit environment, is dis-
cussed. The reader is urged to reference the cited portions
of the COSMAC Microprocessor Manual. The Microkit itself
does not utilize the DMA port or the Interrupt facility.
These are available, however, for added hardware interfaces.
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