The Controller

The controller is an ASM that implements the instruction set of the computer

When the power is first turned on, and after each instruction has completed the controller:

uses the value in the PC to address memory

the value at that memory location is the next instruction

issues a sequence of signals to the architecture corresponding

to the instruction

The input signals to the controller are:

The current instruction

EQZ

The output signals generated by the controller are:

LDABR load a buffer register

sub subtract instead of add

LDACC load the accumulator

OEACC output enable the accumulator

OECONST output enable the constant

C0/C1 select between constant 0 or 1

OEPC output enable the Program Counter

RESET reset line to gates

LDPC load the PC

INCPC increment the PC

WEMEM write enable memory

OEPORT output enable the I/O port

OEMEM output enable memory

LDMAR load memory address register

DISABLE disables the clock (user re-enables it)

Instruction set

The pico-computer only has 8 instructions:

0 LDA operand Load value at location operand into Acc

1 ADD operand Add value at location operand to Acc

2 SUB operand Subtract value at location operand from Acc

3 STA operand Store value in Acc at location operand

4 JPZ operand If value in Acc is 0 jump to operand

otherwise proceed to next instruction

5 IN Input a number from I/O port

6 CLR Load accumulator with 0

7 HLT Halt the clock

So a set of instructions to input three numbers and add them together is:

5 input number to acc

3 100 store acc to location 100

5 input number to acc

3 101 store acc to location 101

5 input number to acc

1 101 add value from location 101

1 100 add value from location 100

7 Halt

Instructions in detail

For all these instructions we may assume that the PC has already been incremented

0 LDA operand

Algorithm:

1 ADD operand

Algorithm:

2 SUB operand

Algorithm:

3 STA operand

Algorithm:

4 JPZ operand

Algorithm:

5 IN

Algorithm:

6 CLR

Algorithm:

7 HALT

Algorithm: