SID hardware initialization sequence - no sound using alternate core

[Knas]

Hi, i'm currently building a SID synthesizer utilizing the MIDIBox SID sid-module and a homebrewn core. Since i have no sound output (not even noise) from my SID i have a few questions:

a) What minimal SID initialization is neede for sound output? The one i'm using right now is going like this:

1. Reset

2. Set DCO1 tune high (reg. 0x01) to app. C3 (0x08)

3. Set DCO1 PWM high (reg 0x03) to 1:1 duty (0x08)

4. Set DCO1 square on and gate on (reg 0x04 to 0x41)

5. Set DCO1 sustain to highest and release to lowest (reg 0x06 to 0xF0)

6. Set main volume (reg 0x18) to highest (0x0F)

I'd guess some of this is redundant, but i tried everything to make it work...

b) What's the expected voltage at the Audio Out Pin and the output transistor respecitvely.

I've doublechecked that the apropriate data is indeed being put on the appropriate pins, i'm using extensive delays both for each high to low CS transition as well as inbetween each data shift. 1Mhz Clock input seems to be fine (shows app. 2,5v on my DMM), it's running hot but that's common as i understand it.

I'm a little worried about groundloops, the SID is hooked up to a switching PSU and the output is connected to audio input on my laptop. Allthough on my scope (which is a home built crap-o-tron soundcard-scope introducing a third PSU in the net) shows nothing weird.

Any help greatly appreciated

Karl

[TK.]

Hi Karl,

your initialisation sequence is correct.

The voltage at the Audio out depends on the SID revision, on my 6581 from CW25/84 it's ca. 5.18 on maximum volume, and 5.25 on minimum volume. Btw.: this is a good check to ensure that register accesses are working - just set the volume to different values between 0x0f and 0x00 and check if the DC offset changes.

I'm not sure if a ground loop could be a problem, normaly they only add AC offset

Best Regards, Thorsten.

[Knas]

Hmm.. that's the same output voltage i get. Weird, as i understand it, the SID *should* be a little noisy right? Mine is dead quiet. Is there by any chance a maximum delay inbetween CS low-to-high or similar? I'm really confused.... I have two SIDs, and one of them *did* work about a year ago. Is there any other voltages i should expect at specific pins?

Karl

[TK.]

I'm not sure about a maximum delay for the CS line, but there shouldn't be an issue. There was a major problem with the MBHP_SID module realted to asynchronous accesses (details see http://www.midibox.org/forum/index.php?topic=5748.0), with the effect, that the gate will be retriggered randomly under certain circumstances. But you should hear a sound, regardless if the SID is clocked synchronously or asynchronously to the microcontroller (if your firmware works with asynch. accesses, you can solve this later...)

No digital background noise: especially on 8580 chips its really quiet (< -70dB). But: have you ever used the SID without the transistor at audio out? Buchi wrote at his website, that he fried a SID by not using it - I took this into account from the beginning - all of my SIDs are still working after more than 3 years usage, and the MBSID is running each day (nice ambient lights ;-))

I don't think that there are other voltages which could be important. Maybe you should doublecheck the caps. Also for trivial errors (e.g. wrong signal polarity).

This reminds me, that the noise at the audio out should be very high during reset - maybe this helps you to check, if anything is comming out of the SID.

Best Regards, Thorsten.