Microcomputer Circuits and Processes

loaded into register A. So the CPU looks first at reg A, gets the address
0101, and stores the data 0011 there, by a WRITE operation.
PC 0 1 1 1 1 MOV Acc --+ M instruction found
0101 0 0 1 1
accumulator
3 data moved
Figure 3.10
MOV Acc- M instruction. Again, note how register A must be interrogated for an
address; this time the address is where the data is to be written.
That completes the instructions we shall need for our program in
the next section, with the exception of one final instruction, which in
fulfilling itself, needs no explanation.
stop STOP 0000
A SIMPLE PROGRAM TO ADD TWO NUMBERS
Table 3.1
In rough outline, a program to add a number 6 10 in memory to another
number 5 10 somewhere else in memory, and put the result 11 10 back
into memory would look like this:
1 Get the number 6 10 and put it into the accumulator.
2 Get the number 5 10 and then add it, putting the result back into the
accumulator.
3 Put the accumulator contents back into memory.
This program is shown nicely assembled in memory in Table 3.1.
The two columns of 4-bit numbers show the instructions/data and the
addresses where they are stored.
EXECUTE cycle number
(These numbers correspond
to those in the titles of
figures 3.15 to 3.25)
Mnemonic
Op-code
or data
(*indicates
data)
Address
Effect of instruction
2
3&4
5
6
MVIA
MOV M-Acc
ADI
MOV Acc-M
STOP
0010
0111*
0110
1111
0101*
0111
0000
0110*
0000
0001
0010
0011
0100
0101
0110
0111
Move the number 0111 into register A, ready to be used as
an address.
Move memory contents into accumulator.
Add the number 0101 (5 10 ) to the accumulator, and put
result in accumulator.
Move accumulator contents into memory.
Stop.
Data 0110 (6 10 ) to be added.
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