EEVblog #1308 - 1970's Intel MCS-85 8085 Design Kit - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: May 28, 2020, 12:29:19 am
content: Will a 1970's era Intel 8085 design kit power up after 40 years?A look at the Intel MCS-85 System Design Kit and some vintage computer and processor history.

author: retrolefty
author_rank: Super Contributor
timestamp: May 28, 2020, 02:40:47 am
content: Nice visit down microprocessor history, well done Dave. I was a Z-80 fanboy during the day.

author: DrG
author_rank: Super Contributor
timestamp: May 28, 2020, 02:48:43 am
content: Enjoyed watching.FYI: The Jan, 1979 Byte magazine features the first of a three part series titled, Build a Computer Controlled Security System for your Home, by Steve Ciarcia (who else?) beginning on p. 56. It used the SDK-85 kit that you were programming. At the end of the article the SDK-85 kit is listed as costing US$250.00.https://archive.org/details/byte-magazine-1979-01/page/n57/mode/2up

author: johnlsenchak
author_rank: Frequent Contributor
timestamp: May 28, 2020, 03:09:26 am
content: Intel System Development Kithttps://en.wikipedia.org/wiki/Intel_System_Development_Kit

author: wilfred
author_rank: Super Contributor
timestamp: May 28, 2020, 03:32:24 am
content: I'd beg to differ that the 8008 was an 8bit version of the 4004. The 8008 was independently developed as a TTL CPU by Computer Terminal Corp in Texas. They then sought to have it built and approached Texas Instruments and Intel to make a microprocessor of equivalent function. One turned out too expensive and late, and the other too slow.A story that is fascinating.https://en.wikipedia.org/wiki/Datapoint_2200P.S. I am enjoying the electronics videos of late.

author: drvtech
author_rank: Regular Contributor
timestamp: May 28, 2020, 10:44:33 am
content: I started work in 1977 and our state-of-the-art system was an MCS-80 Kit (based around the 8080 of course). We had an ASR33 Teletype and we had our own boot loader which we typed in to make it read a program from paper tape. We could also dump to the tape punch. We stored our programs in TTL SN74S472 (I think) bipolar PROMS - one time programmable as they used physical fuses internally. Occasionally we could patch them so long as the patch required adding '1's to the program as they started off all zeroes. Initially we had to take a paper tape over to a nearby company that had a programmer but one of my early jobs was to design and build a programmer for these chips so we could program in house. Later we moved on to the Z80 as our core device as migrating the 8080 code to the Z80 was trivial. About the same time we moved on to 2716 EPROMs (which needed multiple supply rails) This certainly brought back a few memories - thanks Dave.

author: firewalker
author_rank: Super Contributor
timestamp: May 28, 2020, 06:55:21 pm
content: I have this one:Alexander.

author: artag
author_rank: Super Contributor
timestamp: May 28, 2020, 07:46:58 pm
content: 8085 was intel's offering for 8080 upgrades. Like the Z80 it had a less awkward power/clocking requirement than the 8080 and, unusually, an on-chip UART.But it didn't have the Z80's extra registers.I'm not sure how early in the Z80's life it happened but another huge advantage of the Z80 that intel failed to see coming was multiple sources. Zilog, of course, but also Mostek. Were there others ?

author: pickle9000
author_rank: Super Contributor
timestamp: May 28, 2020, 08:49:06 pm
content: I do not miss the "Good ol days".

author: David Hess
author_rank: Super Contributor
timestamp: May 28, 2020, 08:58:07 pm
content: Quote from: artag on May 28, 2020, 07:46:58 pmThe improvement in the power requirements cannot be overstated; the 8085 only required +5 volts while the 8080 also required +12 and −5 volts.The first programming language I learned was 8080 machine code. I did assembly by *hand* on paper forms designed for this purpose.

author: Fungus
author_rank: Super Contributor
timestamp: May 29, 2020, 10:38:42 am
content: If you put ABCDEF on a single row then where do you put the zero?QuoteGood advice

author: drvtech
author_rank: Regular Contributor
timestamp: May 29, 2020, 11:56:17 am
content: Quote from: David Hess on May 28, 2020, 08:58:07 pmSuch luxury - we used graph paper. Got very proficient at remembering the op-codes!

author: coppice
author_rank: Super Contributor
timestamp: May 29, 2020, 12:17:35 pm
content: A lot of the dates shown for these early parts must have been when design began, because they were definitely not being talked about at those times when you met with the vendors.

author: Fungus
author_rank: Super Contributor
timestamp: May 29, 2020, 01:05:00 pm
content: Quote from: David Hess on May 28, 2020, 08:58:07 pmSuch luxury... you must have worked at a large company to get perks like that.I used to do 6502 and Z80 hexadecimal by sight (...on a CRT I could see more than one byte at a time, unlike the board in the video).My first machine code games were written using the hex monitor thing on a Commodore PET after I figured out that pokeing the screen in BASIC was never going to cut it.

author: David Hess
author_rank: Super Contributor
timestamp: May 29, 2020, 03:20:27 pm
content: Quote from: drvtech on May 29, 2020, 11:56:17 amIt was just a preprinted form with spaces for address, opcode, operands, and the hex translation which you had to do yourself.Quote from: Fungus on May 29, 2020, 01:05:00 pmI learned 8080 hex pretty quickly but documenting the assembly was good practice. I still remember some like C3 for JMP.QuoteI used a Prolog PROM programmer to burn the EPROMs directly by typing the hex code into the number pad much like Dave shows.

author: floobydust
author_rank: Super Contributor
timestamp: May 30, 2020, 03:19:15 am
content: This stuff was all very expensive back then, especially after you added RAM and support IC's. A CPU alone was $100 in today's dollars. I thought muxed address/data bus needs more clock cycles per instruction (CPI), so the Z-80 won over that.My first 1978 dev board was a RCA CDP1802 COSMAC ELF 256 bytes of RAM and CMOS, from Quest Electronics. It's the weirdest CPU architecture I've ever seen and still have no idea how to code for it, just brutal.Later I went Z-80 and still have the Assembly Language Programming by Lance Leventhal, programming cards and books. That CPU is a great teacher, it was so much fun knowing "BC" stood for byte-counter...My buddy sold his KIM-1 for $2,000 on eBay, someone has one for sale $9,995 right now. I don't see that much nostalgia for these.Byte Magazine archives

author: coppice
author_rank: Super Contributor
timestamp: May 30, 2020, 10:27:44 am
content: Quote from: Fungus on May 29, 2020, 10:38:42 amLots of microprocessor development kits had 4x4 grids for the hex keys. People were not so used to numeric pads in those days, and the two forms of keypad they were starting to use - DTMF phone and calculators - had completely different layouts. So, arranging a hex pad as an extended numeric pad didn't make as much sense then.

author: bitwelder
author_rank: Super Contributor
timestamp: May 30, 2020, 02:00:44 pm
content: Quote from: DrG on May 28, 2020, 02:48:43 amWhich according some inflation calculator on the 'net should be equivalent to about US$ 980 in 2020.

author: coppice
author_rank: Super Contributor
timestamp: May 30, 2020, 03:45:37 pm
content: Quote from: DrG on May 28, 2020, 02:48:43 amMost microprocessor evaluation kits were around that price, which was quite a lot in those days. It was probably around cost price. Some competitors offered $100 kits for their microprocessors, which were probably shipped at a loss, when they were desperate to get some traction. A LOT of microprocessors appeared between 1974 and 1977, many of which people have long forgotten. Most struggled to get any kind of traction at all, and died quickly. Everyone was pushing hard to get their stuff into actual engineer's hands.

author: jgruszynski
author_rank: Newbie
timestamp: May 30, 2020, 07:10:49 pm
content: I still have one of these. I bought it while I was working at Intel. It was US$100 IIRC with employee discount.That job involved writing production test code in 8085 assembly in 1982. If you have any Intel 27128A EPROMs - all were tested with my code. That job was technically an internship between my junior and senior year of engineering school (EE) but it was "real serious work" not some make work stuff. This was in "Santa Clara 2" back when the corporate HQ was still in Santa Clara 1 (which connected to SC2). Now Intel HQ is in a new building on Mission College Blvd about 1.5 miles from SC1/SC2.There was no mass storage with the MCS85 boards. You either had to enter your entire program in hex when you powered up or you wrote an EPROM. The marketing theory was that you'd use one of the Blue Box Intellec systems to generate code and EPROMs.The "Mass Storage" solution required the Blue Box Intellec, which was only floppy based when I used it to develop production test code.We had two systems at work: one with one floppy and one with two floppies. The latter was the one we fought over because you had to use one 175K disk for your OS (and as you ran the OS it would swap-in code from the floppy) and you could use the 2nd floppy for your code. When you used the 1-floppy version, you had to constantly swap floppy disks on demand alternating between the OS disk and your code disk. The operating system was CP/M though Intel marketed it as "ISIS". The work flow was:Boot ISIS with system disk in floppyLoad your program in edlin(on single floppy system: get prompted to put system disk in)(on single floppy system: system thinks a bit)(on single floppy system: get prompted to put data disk in)(on single floppy system: system writes data to your disk)(on single floppy system: get prompted to put system disk in)Edit codeSave your code(on single floppy system: get prompted to put system disk in)(on single floppy system: system thinks a bit)(on single floppy system: get prompted to put data disk in)(on single floppy system: system writes data to your disk)(on single floppy system: get prompted to put system disk in)Exit editorInvoke assembler on your codeWake 5-10 minutesInvoke EPROM writer command on your binary codeWake 5-10 minutesTake EPROM to tester and insert EPROM into ZIF socket for programmingDebug test program on wafer in wafer proberFind a problem with test program on wafer in wafer proberThink about what could be wrong/Study code/Diagnose problemThrow EPROM into the EPROM eraserGo to step #2 unless program worksprogram works and is completeIt seems insane now but compared to what the MSC-85 board required and what my previous non-floppy CP/M system from the 1970s required, it was luxurious. I haven't really used by MCS-85 in part because even the Intellec solution is painful. In "theory" you can edit memory from the hex keypad but you can't insert code - only overwrite a memory location so generally you have to "know" the exact sequence.One thing with this job was I quickly memorized the hex codes for most of the 8085 instructions. That's because the tester had an instruction pointer that you could single step forward for debugging but the only display was a pair of hex LEDs for address and another for instruction data, so you'd have to know the instructions only from that. I got pretty good at reading 8085 hex. I still remember a few like 0xCD which is CALL.

author: rrinker
author_rank: Super Contributor
timestamp: June 02, 2020, 05:01:12 pm
content: Quote from: floobydust on May 30, 2020, 03:19:15 amSame as my first one. But I don't know what your issue was, the 1802 is SUPER easy to code for. Most programs don;t even need a stack, not with 16 x 16 registers. Brutal? What's brutal about it? The instruction set is super simple, the first nibble for all register operations is the same, with the second nibble referring to which of the 16 registers. SUPER easy. After learning on that, trying to add an assembly routing to a BASIC program on a 6502 Apple II was a super pain. I fail to see, other than the cheap price, why the 6502 is so revered. THAT was a piece of junk, the price was low for a REASON.I DO miss the good old days - it was easy to know ALL of the instruction set of those 8 bit CPUs. Hex keypads on Intel systems are odd - Intel's 8 bit instruction sets are aligned for Octal representation - and I really never did like octal. Hex I can do in my head, octal is just too weird. But today's processors - yeah, just try to know ALL the machine language opcodes. I last did assmebly with 8088's on original PCs, once things got much past that, the instruction sets just got way too complicated to not use a higher level language.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 02, 2020, 05:23:21 pm
content: How much one likes a processor is a lot influenced by what CPU one learns first. The is a tendency to like the one that one start with.For the assembler names / parameters they also use a slightly different organization - about equally good, but the system you learn 2nd looks odd and confusing. It is similar with organizing 16 bit values - high or low byte first.The 6502 is similar in speed to the Z80 at about 4 times the clock. AFAIK the 8080/8085 are a bit slower than the Z80. So performance wise the 8085, 6800, 6502, Z80 were not that far apart. The 6800/6502 used memory mapped IO instead of a separate address space. This can make the HW a little more complicated, but allowed to have a combined RAM+IO chip (6532/6832) to build a relatively simple system. AFAIK the CMOS version of the 6502 came out relatively early too.

author: coppice
author_rank: Super Contributor
timestamp: June 02, 2020, 05:25:32 pm
content: Quote from: rrinker on June 02, 2020, 05:01:12 pmThe 1802 was definitely an easy to use platform for the kind of simple control programs people actually wanted to write for it. The 6502 is only revered because it was the first device many people used, and nostalgia is strong. Th first machine I used was a Honeywell SomethingOrOther. I believe the SomethingOrOther was one of their most popular products, but to me its only interesting quality was that I had some limited access to it to learn and write Fortran code.

author: DrG
author_rank: Super Contributor
timestamp: June 02, 2020, 06:43:33 pm
content: Quote from: coppice on June 02, 2020, 05:25:32 pmBut you have to add in the REASON it was the first that so many used...the reason for the impact that it made....I guess that accessibility can breed reverence if you would not otherwise be able to get involved.6502 price - US$25https://www.eevblog.com/forum/vintage-computing/what-was-you-first-computer/msg2897904/#msg2897904AFAIK, nothing close was cheaper.For example, Z-80 (arguably MUCH more powerful and appearing after the 6502) US$200 (single quantities)https://www.americanradiohistory.com/Archive-Byte/70s/Byte-1976-08.pdf[p.38]

author: coppice
author_rank: Super Contributor
timestamp: June 02, 2020, 07:50:28 pm
content: Quote from: DrG on June 02, 2020, 06:43:33 pmThe prices of one off parts relate to their volume price about as well as a politician's words relate to their actions. People used the 6502 because it was in the box they used. It was in the box because it was cheap, and the original sources - basically MOS Technology and Rockwell - were able to crank them out in adequate numbers (which, or course, relates to them being cheap). The Z80 wasn't all that expensive if you were serious about buying it, and Zilog did well at ramping production (later Zilog wrecked the Z8000 by being very slow at ramping production). The Z80 would never have got to second place in consumer systems, behind the 6502, if it hadn't been pretty cheap.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 02, 2020, 08:17:25 pm
content: As far as I see it from behind the Z80 had 3 strong points: it could run 8080 code and was cheaper than 8080 or 8085. It also had an easier interface, especially when using dynamic RAM. The direct interface to DRAM was an advantage over the 6502 and could easily justify a slightly high price.The price to compare is not just the CPU but also the other chips needed around the system (IO, clock, RAM). In those days the IO chips were also quite expensive.I don't remember the prices from the very early days, but later the Z80 and 6502 were about the same price and the IO chips possibly more expensive. So the CPU price was often only a small fraction of the system. For some odd reason the 8085 stayed quite expensive.

author: DrG
author_rank: Super Contributor
timestamp: June 02, 2020, 08:26:12 pm
content: Quote from: coppice on June 02, 2020, 07:50:28 pm"The prices of one off parts relate to their volume price about as well as a politician's words relate to their actions."Sounds to me like colorful deflection.What exactly were the volume prices for the two chips and when? That information could possibly bolster your point, but it is lacking from your response. The citation I gave said that Z-80 multiple quantity prices (although I don't even think large quantities were available at the time of the article) got it down to US$80 - more than three times the original single unit price of the 6502.BEFORE it was in the box that they used (save the KIM-1 developer board), it was a chip which, I believe, EEs investigated BECAUSE it was cheaper than anything else they could get their hands on. This was before the the Apple and the TRS-80 and so on.What I read you saying is "The Z80 wasn't all that expensive if you were serious about buying it..." What does that mean, "wasn't all that expensive"? Is that some kind of projective test? Is it OK to say that "it wasn't all that cheap" and the statements somehow cancel each other out?What I distinctly do not see you writing is how much the quantity price for the Z-80 was and how that cost compared to the quantity price of the 6502....as well as the 6800 and Intel chips of the time... and of course when the comparison is being made. In a sense, you are talking like the politician that you mock - making the statements without backing it up with any facts. If you had presented some convincing facts, maybe I would change my mind.The 6502 was the cheapest of it's kind and it was accessible. That is amajor reasonthat so many talented people learned and developed with the 6502. Its use in the Pet and the Apple came later. To ignore the price differential and do so without data is simply not credible in my view - not if one wants to offer reasonable interpretations of how the history unfolded the way that it did.But, yes, you are entitled to opinion and I don't have any difficulty with you continuing to respond without convincing evidence.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 02, 2020, 08:54:04 pm
content: AFAIK the 6800 was quite expensive in the early days. A reason why Motorola did not like the 6500.In the same byte Magazine there was a price of some $40 for the 8080A (single - though probably not as much discount for quantities). But you also had extra chips for clock and system control (offered at some $12.50 each). I addition the 8080 still needed 3 supplies - this also adds costs and complicates the board.The Z80 being very new back than, means the price could be just for the very early units, likely going down when more chips are available. Even at $80 the Z80 could compete with a 8080 system when using DRAM that gets away with a single 5 V supply. At least in the beginning the Z80 only needed to be comparable / cheaper than a 8080 system. It looks like the Z80 was also faster than the 8080 - especially with fast memory.Some of the early memories (DRAM and EPROM) also needed an additional voltage. So the extra supply for the 8080 was not that bad and odd. Even the initial C64 series used a video chip with an additional higher supply (AFAIR some 9 V).

author: DrG
author_rank: Super Contributor
timestamp: June 02, 2020, 09:19:34 pm
content: Quote from: Kleinstein on June 02, 2020, 08:54:04 pmI agree with you on all points and consideration (well except that I think you meant that Motorola did not like the 6502, not the 6500).I think that you are right that the introductory price for the Z-80 as quoted was likely for very new units. On the otherhand, the 6502 introductory price of $25 could be viewed in the same way.I'm really not all that knowledgeable about the retro history, but because I was there (I mean alive not as a player), it interests me.The impression that I get is that the 6502 actuallystarteda price war. In a few years, I think that the fiscal landscape had changed a great deal - but that is also a few years of development.https://en.wikipedia.org/wiki/MOS_Technology_6502This threadhttps://retrocomputing.stackexchange.com/questions/2760/how-much-did-the-6502-and-z80-costhas some interesting "answers". I would love to see a hard-core database of prices and quantities and dates.Nevertheless, I maintain that integral to the impact and popularity of the 6502 was soundly anchored in it's low initial price. If you build it, they will come...and if you sell it cheaply, they will develop.

author: floobydust
author_rank: Super Contributor
timestamp: June 02, 2020, 11:34:58 pm
content: 1802, six rad-hardened used in theGalileo spacecraftand it's the onlyMCUMPU with a SEX op-codeI don't remember it all but the 1802 concepts were difficult - any register can be the Program Counter, you can't load immediate- everything uses a register as a pointer. Having the return at the beginning of a subroutine? It is more efficient with multiple operations- but when I was a kid, it was too tough to figure out.Code copy pasta fromhttps://www.atarimagazines.com/computeii/issue3/page52.phpCode:6502AD 3412LDA ADDR1; READ MEMORY1802F8 12LDI A.1 (ADDR1); SET UPB8PHI R8; R8 TO POINT TOF8 34LDI A.0 (ADDR1); THE DESIREDA8PLO R8; MEMORY ADDRESS08LDN R8; READ MEMORY;***************************************; 1802 subr callD7SEP R7; GO TO QSUB; 1802 subr QSUBD0QRET: SEP R0; RETURN TO MAIN PROGRAMCDQSUB: LSQ; IF Q IS SET, SKIP 2 BYTES7BSEQ; SET Q38NBR; SKIP A BYTE76REQ; RESET Q30 00BR QRET; GO RETURN

author: coppice
author_rank: Super Contributor
timestamp: June 02, 2020, 11:43:31 pm
content: Quote from: floobydust on June 02, 2020, 11:34:58 pmThe 1802 is only an MPU, not an MCU. Its not the only one with a SEX op-code. Several others, like the 6809, have them.

author: floobydust
author_rank: Super Contributor
timestamp: June 03, 2020, 12:15:26 am
content: OK fixed

author: EEVblog
author_rank: Unknown
timestamp: June 03, 2020, 04:05:58 am
content: Quote from: DrG on June 02, 2020, 09:19:34 pmIt was. They famously sold them out of glass jars at a trade show for $25 a pophttps://spectrum.ieee.org/tech-history/silicon-revolution/chip-hall-of-fame-mos-technology-6502-microprocessorNot sure if Chuck mentioned that on our podcast:https://theamphour.com/241-an-interview-with-chuck-peddle-charismatic-chipmaking-coryphaeus/

author: retrolefty
author_rank: Super Contributor
timestamp: June 03, 2020, 10:44:25 am
content: Quote from: EEVblog on June 03, 2020, 04:05:58 amI was told by no other then the Woz was that the reason he chose the 6502 was indeed because he picked one up for $25 at a bay area computer show. I asked Steve Jobs the same question be gave me some story about upgrade potential, always the marketeer even at the start. This was when they were driving around the bay area selling their Apple (1) at small early computer groups and clubs.

author: DrG
author_rank: Super Contributor
timestamp: June 03, 2020, 02:33:57 pm
content: Here is a very interesting interview with Ralph Ungermann, Federico Faggin, and Masatoshi Shima (3 of the 11 people that were Zilog in 1976) about the creation of the Z-80 and its early days.http://archive.computerhistory.org/resources/text/Oral_History/Zilog_Z80/102658073.05.01.pdfTurns out that they did, indeed, sell a few of their first chips for US$200...Ungermann: We went after the PC business as we know it today. And we brought our prices down to allow us to do that very quickly. When we came out with the product, we priced the Z80 at $200 a chip, and it took us just a few days to understand from our customers that they needed a lower price to be able to go after the market. However, we also had a number of system companies that were thought that they could get the IBM software to run on the Z80. They could crack a lot of IBM markets, but that of course, didn’t ever happen, because the Z80 was not designed to compete with a mainframe.Faggin: Yeah, one of the first customers that we had was Cromemco In fact, Roger Mellon came to the office and I remember personally selling him one Z80 for $200, and Ralph didn’t say it, but NEC was actually our first customer, and I think you sold the Z80 to the competition. <laughs>Ungermann: When we were packaging the product up for shipment, somebody knocked on the door of the office and it was an NEC guy with four $100 bills for two chips. And then right after that a very successful Japanese computer company came in with four $200 bills. That was just the start of the copying.There is an excerpt about their strategy against copying. I don't completely understand it (I don't understand it at all). Anybody that could explain a bit?Faggin: Yes, we were concerned about others copying the Z80. So I was trying to figure what we could do that that would be effective, and that’s when I came across an idea that if we use the depletion load the mask that doesn’t leave any trace, then I could create depletion load devices that look like enhancement mode devices. And by doing that we could trick the customer into believing that a certain logic was implemented, when it was not. Then I told Shima, “Shima, this is the idea how to implement traps. Put traps, you know, figure out how to do the worst possible traps that you can imagine,” and then Shima with his mind, that was steel mind, was able to actually figure out a bunch of traps that he could talk about.Anyways, it is a long an interesting interview and kudos to Computer History Museumhttps://computerhistory.org/

author: Kleinstein
author_rank: Super Contributor
timestamp: June 03, 2020, 03:10:49 pm
content: The anti copy traps somehow did not work that well - there was a 1:1 copy of the Z80 in eastern Germany.

author: David Hess
author_rank: Super Contributor
timestamp: June 03, 2020, 04:40:11 pm
content: Quote from: Kleinstein on June 02, 2020, 05:23:21 pmThe raw clock rate is not very informative because it is multiplied by the number of internal phases. So a 4 MHz Z80 is comparable to a 2 MHz 6502 because the former uses 4 phases and the later uses 2, and then you have to include how many clock phases are used for memory access. A 4 MHz 6502 would require much faster memory than a 4 MHz Z80.And the 6502 and Z80 are not very different compared to some other processors of the time. Some of the 8080 derived microcontrollers used 12 clock phases!

author: floobydust
author_rank: Super Contributor
timestamp: June 03, 2020, 10:19:26 pm
content: Comparing CPU's throughput is very complicated. An entire university course on that, math between different architectures was no fun. RISC vs CISC and % of applications doing loops or bulk memory transfers, support for DRAM refresh also affects your benchmark results. It can be an endless argument.Looking at how many clock cycles per instruction including the mux'd address/data bus, you still end up against how efficient code is with 16 registers verses say three A,X,Y.I remember the 68000 is a slow dog with DTACK it needed an extra clock cycle- that sadly put it to pasture.

author: Fungus
author_rank: Super Contributor
timestamp: June 04, 2020, 06:40:21 am
content: Quote from: David Hess on June 03, 2020, 04:40:11 pmIMHO a 4MHz Z80 would run like more like a 1.5MHz 6502, despite the 6502 only having 3 registers, etc.

author: DrG
author_rank: Super Contributor
timestamp: June 04, 2020, 12:33:55 pm
content: I learned 6502 Asm before Z80 Asm and this was the early 80s. To me, the Z80 instruction set was richer, a little more complicated, but, again, to me, seemed much more powerful.A big thrill was to run an asm program to white out the screen on the TRS-80 and compared to the BASIC version, did so in a flash.I never had any real experience with the 8080, but the word at the time was that the Z80 was a souped up version of the 8080. My myopic hobbyist view at the time was that there was no point in learning 8080 with the Z80 and the TRS-80 M1. That later changed with the 8086/8088 and IBM and so on.One point really stuck out and that was the Z80 “prime” registers. AF BC DE HL had ‘shadow registers’, AF’ BC’ DE’ and HL’ and you could exchange values between the registers using a single instruction (EX and EXX). Ideally suited for interrupt processing I guess. I only tested them and never really did use them otherwise, but I thought it was an extraordinary concept and I don’t remember hearing that any processors at the time had anything like that. Didn't know it then, but I was learning about banked registers.I also found out, if I am recalling correctly, that the TRS-80 M1 ROMS never used the prime registers at all. Further, speaking of those ROMS, they were dissected at great length and that was exciting.A few years later, I encountered the PIC and when looking at the instruction set at first, I just had a massive WTF? …but with some practice…those too started making sense….but they had so little memory

author: DrG
author_rank: Super Contributor
timestamp: June 04, 2020, 12:36:47 pm
content: More old man reminiscing…..Another big difference between the 6502 and the Z80 in my eyes was regarding, what hobbyists at the time called, “real world interfacing”. That was an incredibly exciting concept – you could turn stuff on and off. The 6502 was “stuck” with memory mapped I/O but the Z80 had an IN and OUT signal that you could use with the lower 8 bits of the address bus and you had 255 I/O ports without messing up the 64K address space.When I entered Grad school I was introduced to these 6 foot racks of electromechanical equipment for instrumentation. We had to hand wire and make all of these lock up relays and pulse formers and pre-determining counters and a whole bunch of crap. People would walk by the lab and think that we were the University phone company from the cacophony of clicking and flashing lights.The situation was a great motivator to figure out how a few lines of code and a little interfacing could replace all of those parts…and those racks became programs before graduating.Chasing that capability was why I learned anything at all about TTL logic. The idea of tri-state logic seemed absolutely correct to me. The how of my learning was mostly due to folks like Steve Ciarcia and Don Lancaster and a host of others who wrote their hearts out.Not being an EE and being completely immersed in a very different profession, I would, later, for relaxation, sequester myself in the back of the library (where the old books and some overstuffed furniture was [shout out to all those greatly tolerant librarians]) with BYTE and KILOBAUD (and also the mathematical recreations column of Scientific American) and all of the, relatively few, books that they had on the subject. It was fun in a very refreshing way.OK, back to the present.

author: David Hess
author_rank: Super Contributor
timestamp: June 04, 2020, 09:15:02 pm
content: Quote from: Fungus on June 04, 2020, 06:40:21 amFor simplicity I left out that some Z80 instructions are only 3 phases and left out ISA differences. Based on memory cycle time which is a hard limit, A Z80 with a higher clock rate should be compared to the 6502.This is also why older CPU microarchitectures do not scale up indefinitely. At some point, a longer load-to-use latency is needed to work within the memory access time which requires a change in microarchitecture.

author: floobydust
author_rank: Super Contributor
timestamp: June 04, 2020, 11:40:53 pm
content: What's this 6502 does pre-fetch? That has extra nerd appeal

author: HKJ
author_rank: Super Contributor
timestamp: June 06, 2020, 04:19:05 am
content: The Z80 needed 4 clock cycles for the basic instructions, some of the more specials ones need up to 20 clock cycles. Then there was the block instructions that could use 1000's of clock cycles, but could be interrupted, they where extremely fast to move or search memory (for the time).

author: Fungus
author_rank: Super Contributor
timestamp: June 06, 2020, 09:51:25 am
content: Quote from: HKJ on June 06, 2020, 04:19:05 amA NOP on a Z80 was (is?) 4 clock cycles.Quote from: HKJ on June 06, 2020, 04:19:05 amBut it's much faster to do multiple LDI instructions than a single LDIR.LDI=16 cyclesLIDR=21 cycles per byte, except the last byte which is 16 cycles.Moral: Unroll those loops!

author: HKJ
author_rank: Super Contributor
timestamp: June 06, 2020, 10:40:54 am
content: Quote from: Fungus on June 06, 2020, 09:51:25 amUnroll a loop to scroll a 4kbyte screen memory? no thanks.Try doing either of that above on a 8080 or 8085. It very long time ago I have played with either processor, but these types of operations was much faster on the Z80. It also had a nice 16bit register plus offset addressing mode (IX+offset), the instruction was slow (As far as I remember it was also about 20 clock cycles), but again faster than doing something similar on a 8080/8085.

author: Fungus
author_rank: Super Contributor
timestamp: June 06, 2020, 11:17:39 am
content: Quote from: HKJ on June 06, 2020, 10:40:54 amYou can unroll it as far as 32 byte chunks (for example), the savings will bealmostthe same.Fun facts:* On the computers with Z80+TMS9918 video chip (eg., MSX) the same trick can be used with OUTI instead of OUTIR to update the screen.* Uridium (a C64 game) really did unroll a loop to copy an entire screen of data (40x25 = 1000 bytes)Quote from: HKJ on June 06, 2020, 10:40:54 amThe IX/IY addressing modes added 12 clock cycles vs. the equivalent HL modes (two extra bytes of instruction fetched, plus offset math). Definitely a thing to be avoided in loops.

author: Bassman59
author_rank: Super Contributor
timestamp: June 10, 2020, 12:35:04 am
content: Quote from: EEVblog on May 28, 2020, 12:29:19 amThis exact kit was the standard for a lab class in computer architecture and program that I took as a junior at Stevens Institute of Technology (Hoboken, NJ) in 1986. Even though by this point "better" processors were widely available, for purposes of learning programming (in assembly, of course) and architecture it was fine.Except there was the one time in class and my lab partner and I could not get the kit to do anything, and we soon came to the realization: "this thing is broken." Of course this was back in the days before everyone had a 'scope on their bench, and we didn't have any other such tools (not even a meter) in the classroom, so when we told the instructors that the kit was broken, they didn't believe us and told us our program didn't work. After a few heated minutes of back and forth, I finally said, "Let's take this kit down to the basement and let Chris look at it."This basement lab was where proper benches were set up and you could check out test equipment (Simpson meters! HP 'scopes with tubes! Power supplies!). The person who ran the lab was this hulking big guy called Chris, who had this Van Dyke beard and always worse (American) football jerseys and sat at a desk inside the cage where the gear was kept. He was the sort of person who didn't take shit and had no time for idiots, but if you came to him with honest questions and concerns, he'd go over and above to help you. I knew him from various other classes and such, so when the instructors and I got to the lab with the 8085 kit and I said, "This doesn't work and they don't believe me," he immediately took it to the bench, pulled off the cover, plugged it in, and metered a few things and said, "he's right, the thing doesn't work." He then pulled another kit from a shelf and handed it to me. The instructors were pissed, of course, but since not finishing the day's project meant that your grade got docked, well, I didn't care. With the new kit in hand, I went back to the classroom, and finished the project.And I've been playing with little micros ever since.

author: alank2
author_rank: Super Contributor
timestamp: June 25, 2020, 02:49:34 pm
content: 1A consumption! Wow. I really enjoyed the video.I'm working on an emulation trainer based on an AVR mega1284 that will emulate the 8080/8085. i chose the same 4x4 hex key layout - I just can't think of a better way to do it.