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Sega 315-5066 pinouts (custom chip in SG-1000 II)Posted: Sun Nov 27, 2011 3:09 am
Last edited by honestbob on Wed Nov 30, 2011 9:37 pm; edited 5 times in total
Here are the pinouts for the Sega 315-5066 chip in the SG-1000 II. This is a combination TMS99XX compatible video chip and SN76489 sound chip all rolled into one.
Sega 315-5066 pinout
Note: IC11 and IC12 are NEC D41416C-15 - 16K x 4 DRAM. This provides the 16K of VRAM for the 315-5066 chip. Pin 1 /OE is permanently wired low.
Note 2: NC means 'Not Connected', although it is hard to be certain on that as the board has a second layer of white soldermask or silkscreen on top of the green soldermask, so it is hard to see which traces go to which IC pins.
Note 3: There are several outputs for the custom RGB signals which go to unused solder points on the PCB so it looks like you can modify to suit other video systems if you know what you are doing (currently NTSC RF).
Note 4: There is also a component labelled IO 73863 T.Q.C. connected to the 315-5066 and I have no idea what that is :)
[Edit - this is a 10.73863 MHz crystal oscillator]
1: pin 2 IC 11 I/O1 (VRAM)
2: pin 3 IC 11 I/O2 (VRAM)
3: pin 15 IC 11 I/O3 (VRAM)
4: pin 17 IC 11 I/04 (VRAM)
5: pin 2 IC 12 I/O1 (VRAM)
6: pin 3 IC 12 I/O2 (VRAM)
7: pin 15 IC 12 I/O3 (VRAM)
8: pin 17 IC 12 I/O4 (VRAM)
10: pin 4 of RF modulator (audio output)
12: pin 1 input to LS32 also pin 11 on expansion edge connector
(the other input is Z80 /RD)
the output of this feeds into pin 4 on the LS32 and that is ORed with
input from pin 22 on the Expansion edge connector. The output of that
goes to pin 15 on IC8 LS257
18: pin 13 LS32 OR gate (ORed with DSRAM to give the /CE for 2KB onboard SRAM)
19: /CEROM2 signal to cartridge port pin B04
20: input from RESET / Hold switch
21: Z80 /NMI (pin 17)
22: Z80 /MREQ (pin 19)
23: C1 + lead, /RESET Z80 (pin 26)
24: Z80 /RFSH (pin 28)
25: Z80 A14
26: Z80 A15 (pin 5)
27: R on PCB (unused solder point)
28: G on PCB (unused solder point)
29: B on PCB (unused solder point)
30: composite video output for RF Modulator pin 3
connected to TP1 on PCB (unused solder point), R40 127 ohm pull down resistor to GND, C16 + lead
pin 3 of the RF Modulator is connected to the negative lead of C16
31: CSYNC on PCB (unused solder point)
33: 10.73863 MHz crysal oscillator. Right pin when looking from component side of PCB
34: other lead of 10.73863 MHz crysal oscillator , C12
35: Z80 /CLK (pin 6)
36: pin 5 IC11 & IC12 /RAS (VRAM)
37: pin 16 IC11 & IC12 /CAS (VRAM)
38: pin 4 IC11 & IC12 /WE (VRAM)
39: pin 14 IC11 & IC12 A0 (VRAM)
40: pin 13 IC11 & IC12 A1 (VRAM)
41: pin 12 IC11 & IC12 A2 (VRAM)
42: pin 11 IC11 & IC12 A3 (VRAM)
43: pin 8 IC11 & IC12 A4 (VRAM)
44: pin 7 IC11 & IC12 A5 (VRAM)
45: pin 6 IC11 & IC12 A6 (VRAM)
46: pin 10 IC11 & IC12 A7 (VRAM)
48: VQO on PCB (unused solder point)
50: pin 10 on expansion connector /RD
51: pin 9 on expansion connector /WR
52: pin 7 on expansion connector /IOREQ
53: Z80 A0 and pin 1 of both LS257s
54: Z80 A6 (cartridge A07)
55: Z80 A7
56: Z80 /INT (pin 16)
57: Z80 D0
58: Z80 D1
59: Z80 D2
60: Z80 D3
61: Z80 D4
62: Z80 D5
63: Z80 D6
64: Z80 D7
||Posted: Tue Nov 29, 2011 2:11 am|
This weird looking thing is a 10.73863 MHz crystal oscillator.
On the expansion connector pin 11 is KBSEL#, so that would make pin 22 the active-high joystick port disable signal (JYDS/KILLGA).
The pair of '257s likely makes up the input ports then, with the select input coming from A0 to decode pairs like C0/C1 or DC/DD.
This is fascinating as it is identical to the I/O implementation in the Mark III. You can really see the evolution of the SG-1000 becoming the Mark III with this system.
This is probably Z80 A0.
It seems like there is no composite video output, so I guess there must be components on the board to do RGB to composite conversion to feed the RF modulator?
Thanks for doing all this hard work!
SG-1000 II Photos and 315-5066 Pinout CorrectionsPosted: Tue Nov 29, 2011 5:45 pm
Last edited by honestbob on Wed Nov 30, 2011 9:42 pm; edited 1 time in total
Correct. Pin 53 is also connected to Z80 A0 (pin 30)
Thanks. On reflection that does look like a '10' rather than 'IO'. Oops :)
I originally had pin 10 as NC. This in fact feeds to the RF modulator, so I'd guess this is the composite video output. Those unused solder points on the board with the seperate RGB signals etc. are not connected to the RF modulator. I guess this was Sega working on a single chip which could be used for all markets with some external hardware mods?
pin 1 of rf modulator goes to high / low channel switch
pin 2 of rf modulator is +5v
pin 3 of rf modulator is R41 330 ohm (which goes to C16 negative lead) and is in series with R42 1760 ohm to GND. The positive side of C16 is that unused TP1 solder point which is connected to pin 30 on the 315-5066.
[Edit - this is the composite video feed from the Sega 315-5066 pin 30]
pin 4 of rf modulator goes to pin 10 of Sega 315-5066
[Edit - this is the audio feed]
I will correct the original post.
No worries :)
I managed to get the heat shield off, so here is another piccy showing the RF modulator, plus better high res photos of the SG-1000 II PCB.
And just for reference, here are the continuity tests I did on the expansion port
SG-1000 II Expansion Port Pinout
5: Z80 A2
11: pin 12 on Sega 315-5066 and pin 1 on OR gate
22: from pin 5 of LS32 OR gate (input) (OR gate pin 6 output goes to pin 15 on IC8 LS257)
the other input is pin 1 OR pin 2
pin 1 is from pin 12 of Sega 315-5066 chip. pin 2 is /RD
||Posted: Tue Nov 29, 2011 7:09 pm|
If pin 10 is the composite video output, then I guess pin 30 is the audio output (just judging by the caps and stuff attached to it).
It could be. The composite video output would definitely not work if there was a PAL mode, but in that case the RGB output could be used. I don't know if there is any easy way to determine which pin is a potential NTSC/PAL select input. It may not even have one.
Very nice, I was wondering where the other '257 was at.
Good to see this is compatible with the MK3 expansion port.
If you've had a chance to look at the cartridge port, does Z80 /M1 go to pin B20? No rush though, you've done plenty already. :)
||Posted: Tue Nov 29, 2011 8:25 pm|
I posted the cartridge port connections on your original pinout thread that I side-tracked into a discussion on the SC-3000 keyboard :) See the last post on
I have B20 as NC, but I will recheck that tonight.
[Edit - correct. B20 is not connected to anything]
I wondered about that. The only issue is that pin 30 on the 315-5066 is connected to the positive lead of C16 and pin 3 of the RF modulator is connected to the negative lead of C16 through R41, but there are no direct connections between pin 30 on the 315-5066 and the RF modulator. I thought the main purpose of caps in general was a smoothing effect, so that couldn't be used to transmit the audio signal to the RF modulator, right? Or could the audio signal already be encoded in the output from pin 10? Does anyone know what pin 3 and pin 4 on the modulator are supposed to do? I can't find a datasheet for this modulator.
[Edit - we've obviously hit the limits on my understanding of basic electronics :) But I think I see how the link from pin 30 to the modulator works - I'm guessing the cap and resistors together work to translate the digital signal to some sort of analog waveform input into the modulator. Anyone with a better grasp of electronic circuits please feel free to correct]
Those pin 3 connections to the RF modulator didn't make much sense to me when I looked at it this morning, so I will recheck those connections tonight to see if I've missed anything.
[Edit - yes, that is how it is wired up. Nothing else seems to be connected to pin 30 of the 315-5066 or to pin 3 of the rf modulator. The only other bit I missed is that the rf modulator case mount points provide the ground signal to the modulator, so pin 3 & 4 are the only inputs AFAIK)
||Posted: Wed Nov 30, 2011 5:43 pm|
OK, thanks for confirming that and documenting the cartridge pin connections. I wrote that B30 was connected to /M1 for the SC-1000 in the pin list, but now I find that highly suspect. I'll examine the PCB scan again and double check the connections.
IIRC for AC signals the capacitor removes the DC offset. This is referred to as AC coupling (series capacitor on the output) as opposed to DC coupling (no cap). For consumer audio/video equipment it's all AC coupled I believe.
This sounds right. Check out the RF modulator in the SMS schematic:
It seems to be configured the same way you described, there's a composite video, monaural audio, and +5V input, and the case is used for ground.
||Posted: Wed Nov 30, 2011 8:31 pm|
Thanks. That gives me enough to do a web search to learn more about it :)
On the SMS schematic, pin 3 is video and pin 4 is the audio feed to modulator. Care to take a guess on which is which on the SG-1000 II? Or do I need to post a photo of the internals of the modulator to be sure? Can you pop the top on those easily with a screwdriver? It looks like it is just crimped on.
Also see PCB photo below with labelled connections from 315-5066 to RF Modulator
||Posted: Wed Nov 30, 2011 9:13 pm|
The inside of the RF modulator is very cramped and complicated, so it may be hard to figure out what's what. The top just pops off, though you may need to bend it back into shape to fit it back on securely.
I'm not sure which pin is which on the modulator myself. I suppose narrowing it down to two pins is good enough for trial and error testing when somebody reads this thread while attempting a video mod of some kind.
||Posted: Wed Nov 30, 2011 9:30 pm|
Works for me :) I'll leave the modulator alone then.
||Posted: Wed Nov 30, 2011 9:36 pm|
I just checked that RGB Mod page.
So pin 10 on the 315-5066 is audio, pin 30 on the 315-5066 is the composite video feed.
||Posted: Thu Dec 01, 2011 1:20 am|
It's weird, I checked again and pin B20 really is /M1 on the SG-1000. I used these two pictures to confirm:
It's strange they'd assign /M1 like this for the SG-1000 only, then leave it unused for the SC-3000, SG-1000 II, and Mark-III, only restoring it for the Japanese SMS.
I'll update the pinouts.csv file with your contributions and a footnote about this oddity. :D
||Posted: Sun Oct 18, 2020 7:31 am|
Thank you for all the tracing, I attach a schematic for future reference