pixy

pixy is a simple 32-bit processor with twelve instructions.

pixy can...

• be easily programmed using this assembler.
• support conditional instructions.
• access between 2 and 8 MB of RAM.
  

here are the instructions:

• add <rn>, <rs | value>
• sub <rn>, <rs | value>
• and <rn>, <rs>
• or <rn>, <rs>
• xor <rn>, <rs>
• not <rn>
• b <value>
• mov <rn>, <rs | value>
• load <rn>, [<rs>]
• sto <rs | value>, [<rn>]
• test <rn>, <rs>
• stop

arrangement:

1. top left: clock in
2. middle left: data in
3. bottom left: input enable
4. top right: address out
5. middle right: data out
6. bottom right: output enable

connecting to pixy:

• pick a device you'll be using to store programs and data, i.e. RAM.
• link data in to RAM's data output through a tristate.
• link data out to RAM's data input through a tristate.
• link address out to RAM's address input.
• link clock in to an oscillator. 
• link input and output enables to the tristates.

when the clock starts, the processor will try to execute any instructions found at address 0x0000.

internals:

• the CU uses microcode stored in an EEPROM to implement the instruction set.
• information is transferred between components using a data bus which is wrapped around the circuit.
• programs can access four general purpose registers and RAM. They can also talk to any peripherals connected via memory mapping.
• a FIN signal is used to mark the end of an instruction and save clock cycles.
  
• conditional instructions work by triggering FIN (or not) based on ALU flags.