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Hello, I am trying to identify which I/O ports are NOT used by any of the sega 8 bit consoles (sg1000,sc3000,sms jp/us/pal,game gear).
Specifically, I am interested in I/O ports that are taken by mirrors of other ports.
My research so far lead to this. Are there other ports/mirrors that I am missing?

3F: misc
7E: vcounter
7F: hcounter,psg
BE: vdp
BF: vdp
C0-C1:joypad mirror
DC-DF keyboard and joypad
E4-E9: SF7000
F0-F2: YM2413

The entire IO space is filled with mirrors, you have to unmap something to make space.

I found this, sorry for starting a useless thread ;)
http://www.smspower.org/uploads/Development/smstech-20021112.txt

SMS port map:

$00-$3F : Writes to even addresses go to memory control register.
Writes to odd addresses go to I/O control register.
Reads return the last byte of the instruction which read the port.
$40-$7F : Writes to any address go to the SN76489 PSG.
Reads from even addresses return the V counter.
Reads from odd address return the H counter.
$80-$BF : Writes to even addresses go to the VDP data port.
Writes to odd addresses go to the VDP control port.
Reads from even addresses return the VDP data port contents.
Reads from odd address return the VDP status flags.
$C0-$FF : Writes have no effect.
Reads from even addresses return the I/O port A/B register.
Reads from odd address return the I/O port B/misc. register.

So actually there is some unused space, provided you don't mind that the read and write ports aren't the same.

still I wonder whether writes in the $C0-$FF range are intercepted by the YM2413 on the sms or by the keyboard on the SC-3000 or SG-1000/mark III with SK-1000

Both, you have to disable the IO to write to the FM chip.

Author	Message
kamillebidan Joined: 25 Feb 2013 Posts: 384 Location: Osaka	I/O complete mapping Posted: Thu Dec 22, 2016 5:02 am
	Hello, I am trying to identify which I/O ports are NOT used by any of the sega 8 bit consoles (sg1000,sc3000,sms jp/us/pal,game gear). Specifically, I am interested in I/O ports that are taken by mirrors of other ports. My research so far lead to this. Are there other ports/mirrors that I am missing? 3F: misc 7E: vcounter 7F: hcounter,psg BE: vdp BF: vdp C0-C1:joypad mirror DC-DF keyboard and joypad E4-E9: SF7000 F0-F2: YM2413

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14745 Location: London	Posted: Thu Dec 22, 2016 7:48 am
	The entire IO space is filled with mirrors, you have to unmap something to make space.

kamillebidan Joined: 25 Feb 2013 Posts: 384 Location: Osaka	Posted: Thu Dec 22, 2016 11:27 am
	I found this, sorry for starting a useless thread ;) http://www.smspower.org/uploads/Development/smstech-20021112.txt SMS port map: $00-$3F : Writes to even addresses go to memory control register. Writes to odd addresses go to I/O control register. Reads return the last byte of the instruction which read the port. $40-$7F : Writes to any address go to the SN76489 PSG. Reads from even addresses return the V counter. Reads from odd address return the H counter. $80-$BF : Writes to even addresses go to the VDP data port. Writes to odd addresses go to the VDP control port. Reads from even addresses return the VDP data port contents. Reads from odd address return the VDP status flags. $C0-$FF : Writes have no effect. Reads from even addresses return the I/O port A/B register. Reads from odd address return the I/O port B/misc. register.

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14745 Location: London	Posted: Thu Dec 22, 2016 3:00 pm
	So actually there is some unused space, provided you don't mind that the read and write ports aren't the same.

kamillebidan Joined: 25 Feb 2013 Posts: 384 Location: Osaka	Posted: Sun Dec 25, 2016 11:58 pm
	still I wonder whether writes in the $C0-$FF range are intercepted by the YM2413 on the sms or by the keyboard on the SC-3000 or SG-1000/mark III with SK-1000

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14745 Location: London	Posted: Mon Dec 26, 2016 7:53 am
	Both, you have to disable the IO to write to the FM chip.

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