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NES UNROM, UOROM, SGROM, SNROM project template for ca65 assembler
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SNROM template

This is a minimal working program for the Nintendo Entertainment System using the SGROM, SNROM, UNROM, or UOROM board. It assumes familiarity with nrom-template.

Additional concepts illustrated:

  • initializing the MMC1
  • loading tile data into CHR RAM
  • calls from one PRG bank to another

Setting up the build environment

Building this demo requires cc65, Python, Pillow, GNU Make, and GNU Coreutils. For detailed instructions to set up a build environment, see nrom-template.

Organization of the program

Include files

  • Register definitions and useful macros
  • Global variable and function declarations

Source code files

  • mmc1.s: iNES header and driver for MMC1
  • unrom.s: iNES header and driver for UNROM/UOROM
  • init.s: PPU and CPU I/O initialization code
  • main.s: Main program
  • bankcalltable.s: List of entry points called through a far call (one that goes from one bank to another)
  • chrram.s: CHR RAM data setup
  • bg.s: Background graphics setup
  • player.s: Player sprite graphics setup and movement
  • pads.s: Read the controllers in a DPCM-safe manner
  • ppuclear.s: Useful subroutines for interacting with the S-PPU


  • NESdev Wiki and forum contributors
  • FCEUX team
  • Joe Parsell (Memblers) for getting me into NESdev in the first place
  • Jeremy Chadwick (koitsu) for more code organization tips


The demo is distributed under the following license, based on the GNU All-Permissive License:

Copyright 2011-2016 Damian Yerrick

Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved in all source code copies. This file is offered as-is, without any warranty.

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