{"id":3149,"date":"2025-10-14T16:43:10","date_gmt":"2025-10-14T15:43:10","guid":{"rendered":"https:\/\/www.robertprice.co.uk\/robblog\/?p=3149"},"modified":"2025-10-14T16:43:11","modified_gmt":"2025-10-14T15:43:11","slug":"rc2025-part-3-bit-banging-a-nes-controller-from-basic","status":"publish","type":"post","link":"https:\/\/www.robertprice.co.uk\/robblog\/rc2025-part-3-bit-banging-a-nes-controller-from-basic\/","title":{"rendered":"RC2025 \u2013 Part 3 \u2013 Bit-banging a NES controller from BASIC"},"content":{"rendered":"\n

In my earlier articles, I’ve written about how an NES controller works and designed some hardware for the RC2014 to talk to one.<\/p>\n\n\n\n

Since then, my PCBs have arrived, and I’ve built the RC2014 module. I had to cut the track from RESET I was using to enable one of the chips and wire that to GND. I explained why in my previous post.<\/p>\n\n\n\n

\"RC2014<\/a><\/figure>\n\n\n\n

I’ve given the module IO address 1 using the jumper switches. This means I can talk to it using the MS-Basic commands OUT 1,X for output, and INP(1) for input.<\/p>\n\n\n\n

\"RC2014<\/a><\/figure>\n\n\n\n

As the output from the NES controller is active low, the green LED attached to the Data input is lit unless a button is being pressed. I should probably have wired this so it only lights if a button is being pressed. This is just a cosmetic issue.<\/p>\n\n\n\n

First BASIC program<\/h2>\n\n\n\n

The first thing I need to do to talk to the NES controller is to toggle the Latch line. This is D1. I need to make this go from low to high, then back to low.<\/p>\n\n\n\n

Next, I need to iterate the following 8 times, 1 for each bit. Read the input and toggle the Clock line high to low to get the next bit ready. If I see a zero value on my input, I know a button has been pressed. <\/p>\n\n\n\n

Finally, I restart the program from the beginning. <\/p>\n\n\n\n

10 REM Bit Banging an NES Controller from an RC2014.\n11 REM Robert Price - October 2025.\n20 REM First we toggle the Latch line on D1. \n30 OUT 1,0\n40 OUT 1,2\n50 OUT 1,0\n60 REM Iterate 8 times to get all 8 bits.\n70 FOR I=0 TO 7\n80 REM Get the current bit in D0.\n90 LET A= INP(1)\n100 REM Toggle the Clock line in D0.\n110 OUT 1,1\n120 OUT 1,0\n130 REM If we have a non zero value, then a button has been pressed.\n140 IF A=0 THEN PRINT I\n150 NEXT I\n160 REM loop back to the beginning.\n170 GOTO 10<\/code><\/pre>\n\n\n\n
When I run this code and press a button, the value of I is printed on the terminal.<\/p>\n\n\n\n
Improving the BASIC program<\/h2>\n\n\n\n
Instead of just printing a numeric value, I can print the name of the button being pressed. In my earlier article, I listed what these values were. To do this, I look at the value of variable I, and print what that value actually means.<\/p>\n\n\n\n
10 REM Bit Banging an NES Controller from an RC2014.\n11 REM Robert Price - October 2025.\n20 REM First we toggle the Latch line on D1. \n30 OUT 1,0\n40 OUT 1,2\n50 OUT 1,0\n60 REM Iterate 8 times to get all 8 bits.\n70 FOR I=0 TO 7\n80 REM Get the current bit in D0.\n90 LET A= INP(1)\n100 REM Toggle the Clock line in D0.\n110 OUT 1,1\n120 OUT 1,0\n130 REM If we have a non zero value, then a button has been pressed.\n140 IF A<>0 THEN GOTO 230\n150 IF I=0 THEN PRINT \"A\"\n160 IF I=1 THEN PRINT \"B\"\n170 IF I=2 THEN PRINT \"SELECT\"\n180 IF I=3 THEN PRINT \"START\"\n190 IF I=4 THEN PRINT \"UP\"\n200 IF I=5 THEN PRINT \"DOWN\"\n210 IF I=6 THEN PRINT \"LEFT\"\n220 IF I=7 THEN PRINT \"RIGHT\" \n230 NEXT I\n240 REM loop back to the beginning.\n250 GOTO 10<\/code><\/pre>\n\n\n\n
Running this and pressing a button now prints the name of that button to the terminal.<\/p>\n","protected":false},"excerpt":{"rendered":"
In my earlier articles, I’ve written about how an NES controller works and designed some hardware for the RC2014 to talk to one. Since then, my PCBs have arrived, and I’ve built the RC2014 module. I had to cut the track from RESET I was using to enable one of the chips and wire that … Continue reading “RC2025 \u2013 Part 3 \u2013 Bit-banging a NES controller from BASIC”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":3153,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"inline_featured_image":false,"footnotes":""},"categories":[181,187],"tags":[189,183,117,185],"class_list":["post-3149","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-rc2025","category-retrochallenge","tag-basic","tag-nes-joypad","tag-rc2014","tag-rc2025"],"yoast_head":"\nRC2025 \u2013 Part 3 \u2013 Bit-banging a NES controller from BASIC - Robert Price<\/title>\n<meta name=\"description\" content=\"In this article I use MS-BASIC on an RC2014 computer to talk to an NES controller using bit-banging.\" \/>\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-3-bit-banging-a-nes-controller-from-basic\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"RC2025 \u2013 Part 3 \u2013 Bit-banging a NES controller from BASIC - 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