Each module (Registers, ALU, memory, …) has multiple input bits that control the function of the module: Whether it loads data from the bus, outputs data to the bus, resets the module, which operation it should compute, etc. The name, abbreviation in the schematic and the description of each control bit is listed in the following table:

s/a stands for synchronous/asynchronous

Program Counter (PC)

Abbreviation	Name	s/a	Description
CE	Count Enable	s	Enables incrementing the PC on the next positive clock edge
IE_PC_L	Input Enable PC Low	s	Enables loading data from the bus to the low byte of the PC
IE_PC_H	Input Enable PC High	s	Enables loading data from the bus to the high byte of the PC
OE_PC_L	Output Enable PC Low	a	Enables outputting data from the low byte of the PC to the bus
OE_PC_H	Output Enable PC High	a	Enables outputting data from the high byte of the PC to the bus

A-Register

Abbreviation	Name	s/a	Description
IE_A	Input Enable A	s	Enables loading data from the bus to the A-Register
OE_A	Output Enable A	a	Enables outputting data from the A-Register to the bus

Memory-Address-Register (MAR)

Abbreviation	Name	s/a	Description
IE_MAR_L	Input Enable MAR Low	s	Enables loading data from the bus to the low byte of the MAR
IE_MAR_H	Input Enable MAR High	s	Enables loading data from the bus to the high byte of the MAR

Arithmetic Logic Unit (ALU)

Abbreviation	Name	s/a	Description
OE_ALU	Output Enable ALU	a	Enables outputting the ALU-result to the bus
ALU_SRC	ALU Source	a	Sets the source of the ALU: 0 = arithmetic operation, 1 = bitwise operation
ALU_CIN	ALU Carry In	a	Sets the Carry In for the adders of the ALU
ALU_AOP	ALU Arithmetic Operation	a	Sets the arithmetic operation of the ALU: 0 = ADD 1 = SUB
ALU_BOP[0:2]	ALU Bitwise Operation	a	Sets the bitwise operation of the ALU: 000 = AND 001 = OR 010 = XOR 011 = NOT 100 = SHL 101 = SLR 110 = SAR 111 = ROR

Flags-Register

Abbreviation	Name	s/a	Description
IE_F	Input Enable Flags	s	Enables loading data from the bus to the Flags-Register
OE_F	Output Enable Flags	a	Enables outputting data from the Flags-Register to the bus

Memory

Abbreviation	Name	s/a	Description
MEM_WE	Memory Write Enable	s	Enables writing to RAM
MEM_EN_IO	Memory Enable Input/Output	a	Enables data flow between memory and bus (direction depends on MEM_WE )

Controller

Abbreviation	Name	s/a	Description
RSC	Reset Step Counter	a	Resets the steps counter to zero. This is executed at the end of each instruction to reduce microsteps per instruction.

Temporary-Register (TMP)

Abbreviation	Name	s/a	Description
IE_T	Input Enable TMP	s	Enables loading data from the bus to the TMP-Register
OE_T	Output Enable TMP	a	Enables outputting data from the TMP-Register to the bus

B-Register

Abbreviation	Name	s/a	Description
IE_B	Input Enable B	s	Enables loading data from the bus to the B-Register
OE_B	Output Enable B	a	Enables outputting data from the B-Register to the bus

Instruction-Register (IR)

Abbreviation	Name	s/a	Description
IE_IR	Input Enable Instruction Register	s	Enables loading data from the bus to the Instruction-Register
OE_IR	Output Enable Instruction Register	a	Enables outputting data from the Instruction-Register to the bus

X-Register

Abbreviation	Name	s/a	Description
IE_X	Input Enable X	s	Enables loading data from the bus to the X-Register
OE_X	Output Enable X	a	Enables outputting data from the X-Register to the bus
INC_X	Increment X	s	Increments the X-Register if DEC_X is low
DEC_X	Decrement X	s	Decrements the X-Register if INC_X is low

Page-Register-Buffer-Register (PRB)

Abbreviation	Name	s/a	Description
IE_PRB	Input Enable PRB	s	Enables loading data from the bus to the PRB-Register
OE_PRB	Output Enable PRB	a	Enables outputting data from the PRB-Register to the bus

7-Segment Display

Abbreviation	Name	s/a	Description
IE_7SD	Input Enable 7-Segment Display	s	Enables loading data from the bus to the 7-Segment Display (the data will be displayed immediately)

Stack Pointer (SP)

Abbreviation	Name	s/a	Description
IE_SP_L	Input Enable Stack Pointer Low	s	Enables loading data from the bus to the low byte of the Stack Pointer
IE_SP_H	Input Enable Stack Pointer High	s	Enables loading data from the bus to the high byte of the Stack Pointer
OE_SP_L	Output Enable Stack Pointer Low	a	Enables outputting data from the low byte of the Stack Pointer to the bus
OE_SP_H	Output Enable Stack Pointer High	a	Enables outputting data from the high byte of the Stack Pointer to the bus

LCD

Abbreviation	Name	s/a	Description
LCD_RS	LCD Register Select	a	Chooses between the instruction register (0) and the data register (1) of the LCD-display
LCD_E	LCD Enable	a	Writes the data that is currently present at the data pins