112 tt09-pettit-wokproc-trainer :: Quicker, easier and cheaper to make your own chip!

What is WocProc Trainer?

WocProc Trainer is a partial CPU implementation coded entirely in Wokwi! While it is not a fully functional CPU capable of fetching instructions and running code, it does provide the ALU, registers and opcode deocde for performaing CPU operations when you "feed" it instructions. Turning it into a full CPU would require addition of a Program Counter (PC), execution state machine, flow control opcodes (jump, call, return, conditional branches, etc.), and an interface for fetching opcodes.

How it works

It works by "feeding" it opcodes and data via the ui[7:0] and ui[0] input pins and then executing them by toggling the uio[1] input pin. Some instructions require additional "Immediate Data" to be supplied via the ui[7:0] input pins prior to toggling the uio[1] "execute" input.

The WokProc has an 8-bit accumulator and 4 8-bit working registers and can perform ADD, SUBTRACT and the standard logical functions AND,OR,XOR and NOT, as well as shift left/right operations. It also keeps track of CARRY and ZERO bits to reflect the results of operations.

How to test

Provide a 10KHz clock then issue rst_n pulse.
Select the desired output mode for viewing results. For this testing, set uio_in[5:2] all LOW.

uio_in[2]: Selects 7-Segment (LOW) or binary (HIGH) output format uio_in[4]: Selects auto nibble / digit display (LOW) or manual (HIGH) uio_in[3]: Manual digit select when uio_in[4] is HIGH. uio_in[5]: Selects value to output (LOW = ACC reg, HIGH = new ACC load value)
Monitor the results using the 7-Seg display and uio_out[7:6] bits:

 uio_out[6]: Indicates if CARRY bit is set
 uio_out[7]: Indicates if ZERO bit is set

Perform an addition. After reset, the opcode register contains opcode 0x00, which is A = A + IMM. So supply a binry input value on ui_in[7:0] and toggle the EXECUTE input (uio_in[1]) HIGH then LOW. The 7-Seg display should display the HEX value of the sum.
The first addition just looked like a 'load' since Acc was zero from the reset. Add the value a second time (or supply a different value on ui_in[7:0]) and toggle the EXECUTE input again. The 7-Segment display should show the result of the addiiton.
Load register r0 from the A register. First enter the opcode (7'b1100_0000 from the opcode table) and then toggle the LOAD (ui_in[0]) input HIGH then LOW to load ui_in[7:] to the opcode register. Now toggle the EXECUTE (ui_in[1]) input HIGH then LOW. Register r0 should now contain the value from A.
Test if register r0 was loaded. First clear the Acc register (load opcode 7'b0111_0000 and EXECUTE it). The 7-Seg should show "00.". Now load and execute the opcode to load register r0 to Acc (opcode 7'b0110_0000). The 7-Seg should show the result of the summation that was stored in r0.
Perform a NOT operation on the A register by loading and executing opcode 7'0111_0001. The 7-Seg should show the compliment value of what was in A.
Try additional oerations from the opcode table by loading and executing them. For any opcode that uses IMM data, uio_in[7:0] inputs must be changed to the immediate data AFTER loading the opcode but BEFORE executing it.

Opcodes supported:

Opcode	Operation	Description
0000_0000	A <= A + IMM	Add A + immediate data
0000_1000	A <= A + IMM + Carry	Add with carry A + immediate
0001_0000	A <= A - IMM	Subtract immediate from A
0001_1000	A <= A - IMM - Borrow	Subtract with borrow immediate
0010_00rr	A <= A + R[1:0]	Add register rr to A
0010_10rr	A <= A + R[1:0] + Carry	Add with carry register rr
0011_00rr	A <= A - R[1:0]	Subtract register rr from A
0011_10rr	A <= A - R[1:0] - Borrow	Subtract with borrow register rr
0100_0000	A <= IMM	Load A with immediate data
0110_00rr	A <= R[1:0]	Load A from register rr
0110_01rr	A <= A ^ R[1:0]	XOR A with register rr
0110_10rr	A <= A OR R[1:0]	OR A with register rr
0110_11rr	A <= A & R[1:0]	AND A with register rr
0111_0000	A <= Zero	Clear A
0111_0001	A <= !A	Invert (1's compliment) A`
0111_01rr	A <= !R[1:0]	Load A from rr compliment
0111_1000	Cy <= 0	Clear the carry flag
0111_1001	Cy <= !Cy	Compliment the carry flag
0111_1010	{A, Cy} <= {Cy, A}	Shift right A through Carry
0111_1011	{Cy, A} <= {A, Cy}	Shift left A through Carry
0111_1100	A <= {0, A[7:1]}	Shift right A
0111_1101	A <= {A[6:0], 0}	Shift left A
0111_1110	A <= {A[7], A[7:1]}	Signed shift right A
1000_00rr	R[1:0] <= A + IMM	Load register rr with sum
1001_00rr	R[1:0] <= A - IMM	Load register rr with difference
1010_00rr	R[1:0] <= A + R[1:0]	Load register rr with sum
1011_00rr	R[1:0] <= A - R[1:0]	Load register rr with difference
1100_00rr	R[1:0] <= IMM	Load immediate data to rr
1101_00rr	R[1:0] <= A	Load A to rr
1110_RRrr	R[1:0] <= R[3:2]	Copy register RR to rr

Selecting the Output

The uo_out port is used to display the state of the WocProc trainer. It can display either 7-Segment LED encoded register data or direct binary data.

uio_in[2]	uo_out Format
LOW	7-Segment
HIGH	Binary

The data output to uo_out (either 7-Segment or binary) is selected via the uio_in[5] input:

uio_in[5]	uo_out Data
LOW	Acc Register
HIGH	ALU result (value loaded upon EXECUTE)

For 7-Segment output format, a single digit LED display is used to show both the upper and lower nibble of the selected output data. When the LOWER nibble is being displayed, the 7-Segment Decmial Point (DP) will be illuminted and when the UPPER nibble is displayed, it will be turned off, such as:

F1.

The nibble display can be configured using uio_in[4:3] as follows:

uio_in[4:3]	Displayed Nibble
2'b0x	Auto toggle (counter tuned for 10KHz clock)
2'b10	Lower nibble (plus DP)
2'b11	Upper nibble

Hardware needed:

Dip switches and 7-Segment LED.

#	Input	Output	Bidirectional
0	op/imm[0]	seg_a	load_opcode
1	op/imm[1]	seg_b	execute_opcode
2	op/imm[2]	seg_c	sevenSeg_binary
3	op/imm[3]	seg_d	digit_select
4	op/imm[4]	seg_e	manual_digit
5	op/imm[5]	seg_f	digit_a_reg
6	op/imm[6]	seg_g	carry_out
7	op/imm[7]	seg_dp	zero_out

112 tt09-pettit-wokproc-trainer