{"id":3135,"date":"2025-10-09T22:22:01","date_gmt":"2025-10-09T21:22:01","guid":{"rendered":"https:\/\/www.robertprice.co.uk\/robblog\/?p=3135"},"modified":"2025-10-09T22:22:01","modified_gmt":"2025-10-09T21:22:01","slug":"rc2025-part-2-designing-a-pcb-for-bit-banging-a-nes-controller","status":"publish","type":"post","link":"https:\/\/www.robertprice.co.uk\/robblog\/rc2025-part-2-designing-a-pcb-for-bit-banging-a-nes-controller\/","title":{"rendered":"RC2025 – Part 2 – Designing a PCB for bit-banging a NES controller"},"content":{"rendered":"\n

In the first part of my RetroChallenge, I ended by saying I was planning to bit-bang the data from the NES controller into my RC2014.<\/p>\n\n\n\n

Now it’s time to design a PCB to let me connect the NES controller to the RC2014.<\/p>\n\n\n\n

I’m going to use Z80 IO, but I’m not sure what address yet. I’m going to use a 74HCT688 8-bit comparator to allow myself the ability to select a specific IO port on the Z80. I will use a DIP switch with pull-down resistors so I can change the IO port at will without having to get a new PCB made. The \/IORQ line from the Z80 will be used to enable the 74HCT688.<\/p>\n\n\n\n

I need to send Clock and Latch signals to the NES controller, so I need a way to output data on the Z80 IO port. I will use a 74HCT374 to do this. This will allow me to buffer the data lines from Z80. I will enable output by using a 74HCT02 and NORing the output from the 74HCT688 and the Z80 \/WR line.<\/p>\n\n\n\n

For reading data back to the Z80, I will use a 74HCT245. This will let me put data onto the databus when the correct IO Port is being read. I will use the 74HCT02 to NOR the output of 74HCT688 and the Z80 \/RD line to enable the chip. However, this needs to be inverted to work, so I will just use another NOR gate as a NOT gate to do this.<\/p>\n\n\n\n

I will add LEDs on the input and output lines to the NES controller socket to help with any debugging I may need to do. I will also add plenty of test points to see what is going on during debugging. As there are plenty of unused input and output pins, I will expose these on headers for possible future use.<\/p>\n\n\n\n

\"Bit-banging<\/a><\/figure>\n\n\n\n

I have decided to use the following pins to talk to the NES controller.<\/p>\n\n\n\n

PIN<\/strong><\/td>READ \/ WRITE<\/strong><\/td>NES<\/strong><\/td><\/tr>
D0<\/td>READ<\/td>DATA<\/td><\/tr>
D0<\/td>WRITE<\/td>CLOCK<\/td><\/tr>
D1<\/td>WRITE<\/td>LATCH<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Laying out the PCB<\/h2>\n\n\n\n

I have laid out the PCB using Spencer Owen’s guidelines for RC2014 modules<\/a>.<\/p>\n\n\n\n

The spare output pins have been placed at the top for easy access. The NES controller socket has been placed on the right-hand side, along with the test points for it. The indicator LEDs have been placed above this for visibility.<\/p>\n\n\n\n

I have added a ground plane to the back of the PCB, and let EasyEDA handle the routing for me.<\/p>\n\n\n\n

\"PCB<\/figure>\n\n\n\n

You may have noticed that the diagram is for revision 1.1 of the circuit. 1.0 was essentially the same, but I had the output enable on the 74HCT374 connected to the Z80 \/RST line. The idea being I only want this to present data on the bus if the Z80 wasn’t being reset. This pin is only low on reset, so data was never being presented. I just tied this to GND in revision 1.1.<\/p>\n\n\n\n

Unfortunately, revision 1.0 is the version I sent off to be manufactured, so it will need a bodge when I come to solder up the PCB. The trace from \/RST will need to be cut, and OE will need to be wired to GND.<\/p>\n\n\n\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

In the first part of my RetroChallenge, I ended by saying I was planning to bit-bang the data from the NES controller into my RC2014. Now it’s time to design a PCB to let me connect the NES controller to the RC2014. I’m going to use Z80 IO, but I’m not sure what address yet. … Continue reading “RC2025 – Part 2 – Designing a PCB for bit-banging a NES controller”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":3139,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"inline_featured_image":false,"footnotes":""},"categories":[181,187],"tags":[139,117,185],"class_list":["post-3135","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-rc2025","category-retrochallenge","tag-pcb","tag-rc2014","tag-rc2025"],"yoast_head":"\nRC2025 - Part 2 - Designing a PCB for bit-banging a NES controller - Robert Price<\/title>\n<meta name=\"description\" content=\"Designing a PCB to allow me to bit-bang an NES controller on my RC2014 computer.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.robertprice.co.uk\/robblog\/rc2025-part-2-designing-a-pcb-for-bit-banging-a-nes-controller\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"RC2025 - 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