{"id":3257,"date":"2025-11-03T21:36:49","date_gmt":"2025-11-03T21:36:49","guid":{"rendered":"https:\/\/www.robertprice.co.uk\/robblog\/?p=3257"},"modified":"2025-11-03T21:36:51","modified_gmt":"2025-11-03T21:36:51","slug":"rc2025-part-9-using-a-snes-controller","status":"publish","type":"post","link":"https:\/\/www.robertprice.co.uk\/robblog\/rc2025-part-9-using-a-snes-controller\/","title":{"rendered":"RC2025 \u2013 Part 9 \u2013 Using a SNES controller"},"content":{"rendered":"\n

The RetroChallenge may have finished, but I have a few more things to add.<\/p>\n\n\n\n

Chartreuse on Mastodon<\/a> pointed out that the SNES controller is quite like the NES controller. Instead of returning a single byte, it returns two bytes. The first byte is the same as the NES controller; the second contains extra buttons.<\/p>\n\n\n\n

I wanted to see if my existing work could be easily extended to use a SNES controller, so I bought one on AliExpress<\/a>. I also bought a SNES extension lead<\/a> so I could cut it in half and add Dupont sockets to the wires. This means I could wire it directly to the RC2014 module I designed for the NES controller using one of the debug connectors I added to the PCB.<\/p>\n\n\n\n

The SNES controller uses a different connector, but the pins work in the same way. This diagram shows the 5 pins we are interested in, and how we need to wire them up to the RC2014 NES controller module.<\/p>\n\n\n\n

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

Writing a reusable Z80 routine<\/h2>\n\n\n\n

As there are two bytes being returned, I can’t just call my get_buttons routine<\/a>. This will toggle the Latch twice, so I will never get the extra buttons.<\/p>\n\n\n\n

Instead, I have to toggle Latch one at the start of the routine, and call a cut down version of the original get_buttons routine that reads the 8 bits twice. The first byte returned will be the original NES buttons. The second byte will be the extra buttons on the SNES controller. Instead of returning a single byte in register a, I will instead use register pair de. Register d will hold the NES button data, and register e will hold the SNES button data.<\/p>\n\n\n\n

; SNESController.inc\n; Definitions and subroutine to read SNES controller button states\n; Robert Price - 1st November 2025\n\n\n; The Z80 port address to use for the controller interface.\nNES_PORT    EQU $01\n\n; The bit masks for the controller interface lines.\nCLOCK   EQU $01\nLATCH   EQU $02\nDATA    EQU $01\n\n\n; subroutine to read the NES controller button states.\n; returns the button states in DE registers.\n; register D contains the high byte, and register E the low byte. \n; All other registers are preserved.\n; The high byte is like the NES controller, low has the extra SNES buttons.\nget_buttons:\n        push af           ; save af registers\n        push bc           ; save bc registers\n\n; pulse the LATCH line low to high and back to low again.\n        xor a               ; set a to 0 \n        out (NES_PORT), a\n        ld a, LATCH\n        out (NES_PORT), a\n        xor a               ; set a to 0\n        out (NES_PORT), a\n\n        call .get_buttons\n        ld d, a             ; store the button states in register d\n        call .get_buttons\n        ld e, a             ; store the button states in register e\n\n        pop bc              ; restore bc registers\n        pop af              ; restore af registers\n\n        ret                 ; return to caller with button states in a\n\n\n.get_buttons:\n; setup the loop counter to read 8 buttons.\n        ld b, 8             ; 8 buttons to read. \n\n; now we rebuild the byte into register c. As we are setting all 8 bits,\n; we don't need to worry about clearing c first.\n.loop:\n; read the controller button states\n        in a, (NES_PORT)    ; read the DATA line\n\n; move the DATA bit into register c to rebuild the send byte\n        srl a               ; shift right to get the DATA bit into carry\n        rr c                ; rotate carry into bit 7 of c\n\n; pulse the CLOCK line to read the next button.\n        ld a, CLOCK\n        out (NES_PORT), a\n        xor a               ; set a to 0\n        out (NES_PORT), a\n\n; loop to read all buttons.\n        djnz .loop\n\n; return the button states in register a\n        ld a, c             ; put the final button states in a \n        ret<\/code><\/pre>\n\n\n\n
Using the new Z80 routine<\/h2>\n\n\n\n
To test the new routine, I can use LEDs as before. I have two modules that can display an 8-bit value using LEDs. A RC2014 Digital IO module at IO address 0, and a SC134 module at IO address 2. I will display one returned byte on one of the modules, and the second returned byte on the other module. This can be run using SCM as before.<\/p>\n\n\n\n
 ; A simple button reading program for the RC2014 Z80 computer running SCM\n ; this version outputs the SNES button states to a LED output\n ; Robert Price - 1st November 2025\n\n        ORG $9000\n\n; the Z80 port address to use for the LED output.\n; This expects two Digital IO ports to be connected to the RC2014,\n; one at IO address 0 for the high byte, and one at IO address 2 for the low byte.\nLED_PORT_H  EQU $00\nLED_PORT_L  EQU $02\n\nmain:\n; get the button states from the SNES controller\n        call get_buttons     ; call the get_buttons subroutine\n        ld a, d              ; get the high byte button states\n        cpl                  ; invert the bits in register a so pressed buttons are 1, and unpressed are 0\n        out (LED_PORT_H), a  ; output the button states to the LED port\n\n        ld a, e              ; get the low byte button states\n        cpl                  ; invert the bits in register a so pressed buttons are 1, and unpressed are 0\n        out (LED_PORT_L), a  ; output the button states to the LED port\n\n        jr main              ; repeat forever\n\n        INCLUDE \"SNESController.inc\"\n\n        END<\/code><\/pre>\n\n\n\n
<\/p>\n\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
The RetroChallenge may have finished, but I have a few more things to add. Chartreuse on Mastodon pointed out that the SNES controller is quite like the NES controller. Instead of returning a single byte, it returns two bytes. The first byte is the same as the NES controller; the second contains extra buttons. I … Continue reading “RC2025 \u2013 Part 9 \u2013 Using a SNES controller”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":3267,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"inline_featured_image":false,"footnotes":""},"categories":[181,187],"tags":[183,117,185,197,119],"class_list":["post-3257","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-rc2025","category-retrochallenge","tag-nes-joypad","tag-rc2014","tag-rc2025","tag-snes-controller","tag-z80"],"yoast_head":"\nRC2025 \u2013 Part 9 \u2013 Using a SNES controller - Robert Price<\/title>\n<meta name=\"description\" content=\"Extending the RC2014 NES controller module to use a SNES controller instead, and using Z80 assembly language to read it.\" \/>\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-9-using-a-snes-controller\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"RC2025 \u2013 Part 9 \u2013 Using a SNES controller - 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