Changes from v1.x
- Updated to the v2.0 Architecture and the use of a dedicated common CPU bus for the CPU boards
- The three boards of the v1 ALU have been combined into a single board
Schematics
The General Register Board design is split across four schematics- Common CPU bus connector
- ALU Operations
- ALU flags
- Caps
Common CPU bus connector
The common CPU bus connector is shown below. |
| Common CPU Bus connector |
ALU Operations
The ALU can perform 3 mathematical operations and 3 logical operations.- AND : logical AND (left AND right)
- OR : logical OR (left OR right)
- XOR : logical XOR (left XOR right)
- ADD : mathematical addition without carry (left + right + 0)
- ADC : mathematical addition with carry in from the control register (left + right + C)
- SUB : mathematical subtraction (left - right)
The ALU has 4 input controls
Carry Select Control
SEL_C_IN_1 and SEL_C_IN_2 are used to select the carry input- 0 - ALU carry input is zero
- 1 - ALU carry input is one
- 2 - ALU carry input is taken from the carry flag
- (3 - ALU carry input is zero)
Invert Right Input Control
ALU_INV_R is used to invert the right input for subtraction operations- 0 - do not invert (input xor'd 0)
- 1 - invert (input xor'd with 1)
Operation Selection Control
SEL_ALU_OP_1 and SEL_ALU_Op_2 are used to select the ALU operation to output onto the Z bus.- 0 - OR
- 1 - AND
- 2 - XOR
- 3 - ADD
ALU Output Enable Control
OE_ALU is used to enable the ALU output onto the Z bus- 0 - high Z state
- 1 - output enabled
 |
| ALU Operations |
ALU Flags
The ALU flags circuit calculates the Z (zero) & V (overflow). The C (carry) is calculated by the adder and the N (negative) flag is simply the Z7 output.The overflow flag is only meaningful if two's complement numbers are being added. The output is High to indicate an overflow if the following conditions are met
- Adding two positive numbers and the result is negative; or
- Adding two negative numbers and the result is positive
 | |
| ALU flags |
The ALU flags are always calculated and it is up to the micro-code to determine when they are applicable and should be saved in the ALU flags register for inspection.
PCB board
The PCB board is shown below |
| ALU PCB |
Parts List
Part Value Package Library Position (inch) OrientationC1 0.1uF C050-030X075 rcl (2.05 0.3) R90
C2 0.1uF C050-030X075 rcl (2.6 2.5) R180
C3 0.1uF C050-030X075 rcl (4.8 0.25) R90
C4 0.1uF C050-030X075 rcl (1.15 1.1) R90
C5 0.1uF C050-030X075 rcl (2.4 1.1) R90
C6 10uF E5-5 rcl (5.75 0.25) R90
C7 0.1uF C050-030X075 rcl (3.55 1.1) R90
C8 0.1uF C050-030X075 rcl (4.85 1.1) R90
C9 0.1uF C050-030X075 rcl (1.2 3.75) R180
C10 0.1uF C050-030X075 rcl (2.6 3.75) R180
C11 0.1uF C050-030X075 rcl (3.6 3.75) R180
C12 0.1uF C050-030X075 rcl (4.55 3.75) R180
C13 0.1uF C050-030X075 rcl (5.35 3.6) R180
C14 0.1uF C050-030X075 rcl (5.35 2.6) R180
C15 0.1uF C050-030X075 rcl (1.2 2.55) R180
C16 0.1uF C050-030X075 rcl (3.65 2.5) R180
C17 0.1uF C050-030X075 rcl (4.55 2.5) R180
C18 0.1uF C050-030X075 rcl (5.35 1.4) R180
IC1 74HC08N DIL14 74xx-eu (3.55 3.25) R270
IC2 74HC32N DIL14 74xx-eu (2.55 3.25) R270
IC3 74HC86N DIL14 74xx-eu (4.5 3.25) R270
IC4 74ACT283N DIL16 74xx-eu (1.15 3.2) R270
IC5 74HC86N DIL14 74xx-eu (5.3 3.1) R270
IC6 74HC153N DIL16 74xx-eu (1.9 1.15) R180
IC7 74HC153N DIL16 74xx-eu (0.65 1.15) R180
IC8 74HC86N DIL14 74xx-eu (5.3 2.1) R270
IC9 74HC32N DIL14 74xx-eu (2.55 2) R270
IC10 74HC08N DIL14 74xx-eu (3.6 2) R270
IC11 74HC86N DIL14 74xx-eu (4.5 2) R270
IC12 74ACT283N DIL16 74xx-eu (1.15 2.05) R270
IC13 74HC153N DIL16 74xx-eu (4.3 0.3) R180
IC14 74HC153N DIL16 74xx-eu (3.05 1.15) R180
IC15 74HC153N DIL16 74xx-eu (4.3 1.15) R180
IC16 74HC251N DIL16 74xx-eu (1.5 0.35) R180
IC17 4078N DIL14 40xx (5.3 0.95) R270
X1 MAB64 MAB64 con-vg (6.2 1.95) R0
