SIO-2 vs 85C30: HW & SW

[Michelle Lawson]

While I had always  kind of looked over these two, until I started using them, it appears that these two are pin for pin identical. To me, that implied drop in replacement. Add in that the receive and transmit status bits are the same as well (bit 0 & 2) of Read Register 0, it further supports the 85C30 being able to replace the SIO-2 chip in the Dual SIO-2 card. Am I overlooking some glaring difference per chance? Thanks

[Wayne Warthen]

Hmmm... I don't think they are pin identical.  For example, on the 85C30, pin 8 is /INTACK and on the SIO, pin 8 is /M1.

Thanks, Wayne

[Michelle Lawson]

Well, dang, I thought I had check all the pins. Argg. Guess I'm back to square 1 and will just have to spin a couple of 85C30 boards. Looks like lemonade is gonna get made... Thanks Wayne

[Mark T]

Did you see his thread recently?

https://groups.google.com/g/retro-comp/c/imNsPBJO45s/m/Eo8NfaaqAAAJ

Tadeusz has added a github link.

[Michelle Lawson]

Yep, kinda what I'm building mine off of. My addition is that I want it to be RS232 output levels, and be selectable between DTE/DCE. Funny, I just finished outputting the gerbers for it. It isn't exactly RC2014 compliant, but it's my first time getting something spun for this bus, so.... BTW, comments are welcome, and I have no issue with anyone taking this to make it RC2014 compliant. Thanks

[Ed Silky]

Hi Michelle,

Here is a circuit from a Zilog data book for adapting their 85xx peripherals to the Z80.

You can see how M1- and IORQ- are used to generate the required INTACK- signal.

I see that in your design, you aren't using interrupts. That means that you are going to have to do a lot of polling. Is that what you intend?

-Ed

--
You received this message because you are subscribed to the Google Groups "RC2014-Z80" group.
To unsubscribe from this group and stop receiving emails from it, send an email to rc2014-z80+...@googlegroups.com.
To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/c0904651-7398-46bb-aace-b03757f63959n%40googlegroups.com.

[Ed Silky]

Hi Michelle,

Even if you aren't planning to use interrupts, I would still pull IEI (pin-7) up.

Another change you might consider, to reduce propagation delay (allow this to run with faster systems), rather than feeding U5A from U5B, remove IORQ- from the '138 enable and put it into one of the OR gates, and then use the output of each of the gates for the two low-enables. Like this:

This reduces the 'valid address selected' time at the output of the '138 from 97ns to 75ns, while performing the same decoding.

-Ed

[Ed Silky]

Another option for your decoding is:

This is 1ns slower, but it uses 2 chips rather than 3, and it allows you to select the upper range with a single jumper rather than 3. Of course, the 2x8 header is larger than 3 1x3 headers. Plus, you don't have the spare gates in case you need them for other parts of the circuit. You can use the resistor for the 'PU?' to also pull-up the IEI pin of the SCC.

Also, I tend to design with HCT or AHCT rather than LS. They are similar speed (HCT) and faster (AHCT) while using much less power. For example, the 74HCT138 is also 38ns (when using 5V), but uses 80µA compared to 10mA for the 74LS138.

-Ed

[Michelle Lawson]

Thanks Ed, in fact I'll probably switch out the RS232 drivers for drivers that don't require the charge pump caps; ie, MAX233A.

[Ed Silky]

Okay. I use the MAX232, as they are ~$1, while the MAX233 is $24 (at DigiKey anyway).

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/b526a2e0-a6ca-462c-992c-1c035dfb3e9bn%40googlegroups.com.

[Michelle Lawson]

Well, I see your two LS138s and raise you an LS688...

Yep, the 'A' version is a bit pricey, but Unicorn has the non-A versions for $5.49; plus I already have a couple of the Sipex versions I'm going to be testing this design with before I order boards

[Michelle Lawson]

I forgot to add that the non-A versions are still good up to 120kbps, while the 'A' versions can do up to 200kbps....

[Tadeusz Pycio]

Inexpensive RS232 modules are available that can be connected to any RC2014/RCBus serial transmission module.

[Michelle Lawson]

Yep, I saw those Tadeusz, but most did not have the CTS/RTS lines, and the one's that did were about $25. That and I'd kinda like to keep stuff all on one board; and I really enjoy doing this stuff.

[Ed Silky]

Hi Michelle,

A '688 is a bit pricey (in small quantities), but it does give you the most flexibility. I will say that you can probably use a 6-position sw and just tie R7 (18) to ground and R6 (16) to the PU, since you know that you want IORQ- low and M1- high. That frees up a PU on the 9-pin SIP that you can use for the IEI of the SCC.

I like the SCC, when I worked as an engineer at a company that used a lot of Zilog components (we worked closely with a group of the Zilog engineers), we started using the SCC as soon as they became available. But they do take a bit more support circuitry (or a PAL) if you want to use them with a Z80 with Mode-2 interrupts. Plus, in the eBay market now, they tend to be more expensive than the SIO (0/1/2). Another chip that we used on a couple boards was the Z80-DART (Z08470). The DART is an ASYNC only version of the SIO/0. It is pin compatible, with the SIO SYNCA/B pins (11/29) being NC on the DART.

-Ed

--

You received this message because you are subscribed to the Google Groups "RC2014-Z80" group.
To unsubscribe from this group and stop receiving emails from it, send an email to rc2014-z80+...@googlegroups.com.

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/f610b135-b2e5-446d-b43d-fad12b598909n%40googlegroups.com.

[Michelle Lawson]

Yep Ed, you are correct, but I have bins and bins of all sorts of TTL stuff, most of which I will never use. And, I was also going for low chip and component count. I should know after the first of the year if this actually works. I first need to prototype it in wire wrap, then debug it, before I send things off to get some boards ordered. I'll make a minimum order purchase, but I only need two, and one as a spare, so I'll gladly give the other two away if someone wants to play with them.

[Ed Silky]

Very good.

These days, most of my projects are surface mount, so I typically go straight to PCB. Though I might breadboard small parts of it (on a pluggable breadboard) if I'm not 100% sure about things.

I'll give you a tip - if you use PCBWAY or JLCPCB for your boards, when you put your info in and get a quote, check for a quantity of both 5 and 10. I have found that unless my board is very large and/or more than 4 layers, the price for 10 is the same as the price for 5 (or very, very close).

-Ed

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/323168b7-f59d-42a4-aa98-c2d711ed06d1n%40googlegroups.com.

[Michelle Lawson]

I have been using JCLPCB for my previous stuff (4 I think?), so I will stick with them. Thanks Ed

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/CACc-QnK9oK-L1C-FGrqscsXpbmm0Ymxrj9-wJSHNWZxSyYsEew%40mail.gmail.com.

[Ed Silky]

Do you mean "JLCPCB", or is there also a "JCLPCB"?

I use both PCBWAY and JLCPCB, and prefer the quality from PCBWAY a bit more, but for more than 4 layers JLCPCB is typically less expensive. 

Anyway, for others that might not have had boards made before, check the price for a quantity of 5 and 10. You'll find that often the price for either quantity is the same. Some of my robotics projects use 6 or 8 of the same board, so that's how I found that the price for 5 and 10 is often the same (or very close).

-Ed

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/CANpkXaJzTuXyfB4UKHwYsbNY7O3orhyRo0q%2B0e64cK998qUsvg%40mail.gmail.com.

[Michelle Lawson]

Sorry, it is JLCPCB..... Thanks

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/CACc-QnLAD_TR138bu90G3AYP%3DU%2Bqweoc8TyOqOG%2B8KByRbda7A%40mail.gmail.com.

[Ed Silky]

Hi Michelle,

One thing you might consider is creating a symbol and footprint for the oscillator that allows either the small (8-pin footprint) or the large (14-pin footprint) device to be used. I'm actually somewhat surprised that KiCad doesn't have one in their library. Here is the one I made in use:

 

That opens up more choices when acquiring oscillators.

-Ed

 

[Ed Silky]

Here is my KiCad symbol & footprint for those that asked about it.

[Ed Silky]

Note that I don't connect pins 8&11 (the outputs) in the footprint, I leave that up to you during the layout.

When I first created it, I had them connected in the footprint, but then found that sometimes I wanted the connection on the inside, sometimes the outside, etc. to allow other signals to route through/around it. Unfortunately, that does cause an ERC error, indicating that two outputs are connected together.

-Ed

--

You received this message because you are subscribed to the Google Groups "RC2014-Z80" group.
To unsubscribe from this group and stop receiving emails from it, send an email to rc2014-z80+...@googlegroups.com.

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/9e92460b-d2e1-4415-b23f-e2997298fed2n%40googlegroups.com.

[Dylan Hall]

Hi Michelle, could you explain what J3 and J5 are used for? (labelled “DCE/DTE”)

I’m curious if this is something I can use in my own designs :)

Thanks,

Dylan 

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/196a3ad0-61f7-454a-a2e0-c5190d96b7ccn%40googlegroups.com.

[Michelle Lawson]

Thanks Ed for the symbol and footprint. That will come in very handy. Yep, it is surprising that this isn't already part of the KiCAD package.

Dylan, I put J3 & J4 ini there to account for various surplus DB9 ribbon cable configurations. It can be wired for either DCE or DTE using either male or female pinned connectors.

To view this discussion, visit https://groups.google.com/d/msgid/rc2014-z80/CAPBs7ASMfzs3orJOq6ASmBFpB0qsUa8YCQPyFCEVB6FjthNskg%40mail.gmail.com.