4-Bit Adder and Subtractor: K7-Ad405b/405a/405

[k-7iro]

Isn't there a successor to the K7-Ad403a? It's here.

It's a little late, but I've updated it again. When mute is on, the K7-Ad405b always outputs Overflow Carry off. When both mute mode and subtraction mode are enabled, the K7-Ad405a outputs Overflow Carry 1, but the K7-Ad405b outputs it 0.

Overview

A general-purpose 4-bit adder/subtracter that is the successor to the K7-Ad403a. By "linking" chips, it can also handle addition and subtraction of 8 bits or more. The change from the K7-Ad403a is that an output mute function has been added. I think that this time, we have finally reached the "limit" of the Project Red: Fabrication adder, but if anyone has successfully modified it and added functions, or if anyone has successfully developed an adder/subtracter chip with more functions than this one, please let us know.

Which K7-Ad405 variant should I choose?

Unless there is a specific reason, we recommend using the K7-Ad405b. Mute specifications vary depending on the variant.

• K7-Ad405b (latest): When mute is on, Overflow Carry outputs 0 regardless of the subtraction mode.
• K7-Ad405a: When mute is on, Overflow Carry outputs 0 if subtraction mode is off and 1 if it is on.
• K7-Ad405: Even when mute is on, Overflow Carry works the same as when mute is off.

Images

K7-Ad405b Schematic (Tile Count: 197)

Old Version Schematics

Click to show

K7-Ad405a Schematic (Tile Count: 199)

K7-Ad405 Rev1.2 Schematic (Tile Count: 190)

Example Circuit

Using the chip

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Wiring Description

Common to all variants.

Down (Input)

Color	Function
White	Bit A0 (Lowest Digit)
Orange	Bit A1
Magenta	Bit A2
Light Blue	Bit A3 (Highest Digit)
Yellow	Bit B0 (Lowest Digit)
Lime	Bit B1
Pink	Bit B2
Gray	Bit B3 (Highest Digit)

Up (Output)

Color	Function
White	Bit 0 (Lowest Digit)
Orange	Bit 1
Magenta	Bit 2
Light Blue	Bit 3 (Highest Digit)

Left (Input)

Color	Function
White	Overflow Carry
Orange	Subtraction Mode (Input 1 to Subtract)
Magenta	Mute Mode (Input 1 to Mute)

Right (Output)

Color	Function
White	Overflow Carry
Orange	Subtraction Mode
Magenta	Mute Mode

[MrTJP]

Thanks for sharing! Detailed circuits like this will be super helpful as test cases as some point.