Old and new - apparently a difference of only 306,240.90$
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Modernizing an old computer design is a weird thing. First you strip away all anachronisms and look what's left. In the case of the original Elf from 1976 that was the processor itself. By pure chance, I got hands on a CDP1802B, which also already existed in 1976, but it was the faster version which used to cost more. It hums along at 6MHz without breaking a sweat, giving me almost four times the performance of the original Elf. I don't have any means on the breadboard to carefully monitor the processor's core voltage and temperature, but overclocking the processor is possible and I may yet squeeze considerably more out of very old silicon. Toggle switches (or hex keypads) and LED address and data displays are gone, but there is still an interesting aspect about them. The original Elf had no ROM to boot it. Instead, the switches and displays acted as DMA devices and allowed to enter the program manually before letting the processor start executing anything. A modern Elf can have an all RAM configuration, like the original. Why not copy the contents from a ROM to RAM using the same DMA mechanism after a reset? It's still the same old Elf and no typing involved to get that thing running. Plus keeping the advantage of not having a ROM awkwardly floating around in your 64k memory map. Now, we still need some I/O. For the time being that is a serial port and a VT52 or VT100 terminal (actually an old PC running TeraTerm). That was not part of the old Elf concept, because hooking up a 80$ computer to a terminal that costs at least ten times as much seemed a bit silly. However, that option was added later for those who somehow got their hands on a terminal. The cool thing was, that the Elf never required a UART for serial communication. Serial data was sent and received by the processor itself with carefully timed software routines at 300 baud. Well, Zwölf does it the same way, but I rewrote these routines a little so that they now send and receive at 19200 baud. 38400 baud are possible, but the little processor can't keep up yet when the terminal sends packets of data during a XMODEM upload. The problem is, that there is only very little time to actually do anything with the received data before the UART on the other side already sends the next byte. Still, even at 19200 baud I can load a program faster than with an old C64 floppy drive. Indeed, I'm comfortably in the mid range of the C64's floppy accelerators. Not so bad for a crutch that only has to be sufficient until I have something better. Up to here we
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Modernizing an old computer design is a weird thing. First you strip away all anachronisms and look what's left. In the case of the original Elf from 1976 that was the processor itself. By pure chance, I got hands on a CDP1802B, which also already existed in 1976, but it was the faster version which used to cost more. It hums along at 6MHz without breaking a sweat, giving me almost four times the performance of the original Elf. I don't have any means on the breadboard to carefully monitor the processor's core voltage and temperature, but overclocking the processor is possible and I may yet squeeze considerably more out of very old silicon. Toggle switches (or hex keypads) and LED address and data displays are gone, but there is still an interesting aspect about them. The original Elf had no ROM to boot it. Instead, the switches and displays acted as DMA devices and allowed to enter the program manually before letting the processor start executing anything. A modern Elf can have an all RAM configuration, like the original. Why not copy the contents from a ROM to RAM using the same DMA mechanism after a reset? It's still the same old Elf and no typing involved to get that thing running. Plus keeping the advantage of not having a ROM awkwardly floating around in your 64k memory map. Now, we still need some I/O. For the time being that is a serial port and a VT52 or VT100 terminal (actually an old PC running TeraTerm). That was not part of the old Elf concept, because hooking up a 80$ computer to a terminal that costs at least ten times as much seemed a bit silly. However, that option was added later for those who somehow got their hands on a terminal. The cool thing was, that the Elf never required a UART for serial communication. Serial data was sent and received by the processor itself with carefully timed software routines at 300 baud. Well, Zwölf does it the same way, but I rewrote these routines a little so that they now send and receive at 19200 baud. 38400 baud are possible, but the little processor can't keep up yet when the terminal sends packets of data during a XMODEM upload. The problem is, that there is only very little time to actually do anything with the received data before the UART on the other side already sends the next byte. Still, even at 19200 baud I can load a program faster than with an old C64 floppy drive. Indeed, I'm comfortably in the mid range of the C64's floppy accelerators. Not so bad for a crutch that only has to be sufficient until I have something better. Up to here we
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Modernizing an old computer design is a weird thing. First you strip away all anachronisms and look what's left. In the case of the original Elf from 1976 that was the processor itself. By pure chance, I got hands on a CDP1802B, which also already existed in 1976, but it was the faster version which used to cost more. It hums along at 6MHz without breaking a sweat, giving me almost four times the performance of the original Elf. I don't have any means on the breadboard to carefully monitor the processor's core voltage and temperature, but overclocking the processor is possible and I may yet squeeze considerably more out of very old silicon. Toggle switches (or hex keypads) and LED address and data displays are gone, but there is still an interesting aspect about them. The original Elf had no ROM to boot it. Instead, the switches and displays acted as DMA devices and allowed to enter the program manually before letting the processor start executing anything. A modern Elf can have an all RAM configuration, like the original. Why not copy the contents from a ROM to RAM using the same DMA mechanism after a reset? It's still the same old Elf and no typing involved to get that thing running. Plus keeping the advantage of not having a ROM awkwardly floating around in your 64k memory map. Now, we still need some I/O. For the time being that is a serial port and a VT52 or VT100 terminal (actually an old PC running TeraTerm). That was not part of the old Elf concept, because hooking up a 80$ computer to a terminal that costs at least ten times as much seemed a bit silly. However, that option was added later for those who somehow got their hands on a terminal. The cool thing was, that the Elf never required a UART for serial communication. Serial data was sent and received by the processor itself with carefully timed software routines at 300 baud. Well, Zwölf does it the same way, but I rewrote these routines a little so that they now send and receive at 19200 baud. 38400 baud are possible, but the little processor can't keep up yet when the terminal sends packets of data during a XMODEM upload. The problem is, that there is only very little time to actually do anything with the received data before the UART on the other side already sends the next byte. Still, even at 19200 baud I can load a program faster than with an old C64 floppy drive. Indeed, I'm comfortably in the mid range of the C64's floppy accelerators. Not so bad for a crutch that only has to be sufficient until I have something better. Up to here we
Awesome, you're really making progress. I was looking at some old Popular Electronics last week and astounded at the price of memory, only the rich could afford it. (That definitely wasn't me) I'm getting on with my Z80 stuff and really enjoying it. Created a 24 key keypad board using cherry keys. Cheated though using a 328P to scan and debounce. Created a 7-segment display board...6 segment. Also cheated using a MM7219. Well into writing a monitor program for it. Waiting on parts to create an EEPROM emulator, got the idea from the guy I bought the CPU board from. Have a lot of plans.
The less you need, the more you have. Even a blind squirrel gets a nut...occasionally. JaxCoder.com
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Awesome, you're really making progress. I was looking at some old Popular Electronics last week and astounded at the price of memory, only the rich could afford it. (That definitely wasn't me) I'm getting on with my Z80 stuff and really enjoying it. Created a 24 key keypad board using cherry keys. Cheated though using a 328P to scan and debounce. Created a 7-segment display board...6 segment. Also cheated using a MM7219. Well into writing a monitor program for it. Waiting on parts to create an EEPROM emulator, got the idea from the guy I bought the CPU board from. Have a lot of plans.
The less you need, the more you have. Even a blind squirrel gets a nut...occasionally. JaxCoder.com
I remember an ad for a 64K S-100 bus memory board for $1495. I couldn't imagine needing that much RAM. Crap, I use icons now bigger than that...
Software Zen:
delete this; -
I remember an ad for a 64K S-100 bus memory board for $1495. I couldn't imagine needing that much RAM. Crap, I use icons now bigger than that...
Software Zen:
delete this;I hear ya...and could you image surfing on a 1200 baud modem. Take 24 hours to load a page. :)
The less you need, the more you have. Even a blind squirrel gets a nut...occasionally. JaxCoder.com
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I hear ya...and could you image surfing on a 1200 baud modem. Take 24 hours to load a page. :)
The less you need, the more you have. Even a blind squirrel gets a nut...occasionally. JaxCoder.com
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Mike Hankey wrote:
a 1200 baud modem
Back in 1991/2 that's what I had to use to connect between my PC in the London office, and the system in Louisville, CO. Made customer support quite a challenge.
I can imagine that was a challenge. I tried to do the old BBS's with a 1200 and I remember that being enough of a challenge that I didn't do it long.
The less you need, the more you have. Even a blind squirrel gets a nut...occasionally. JaxCoder.com
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I remember an ad for a 64K S-100 bus memory board for $1495. I couldn't imagine needing that much RAM. Crap, I use icons now bigger than that...
Software Zen:
delete this; -
I remember paying a fortune just to upgrade my 8k PET to 16k!
- I would love to change the world, but they won’t give me the source code.
I have a 'fat' TRS-80 Model 100[^], in that I spent $150 to expand it from the original 24K to a full, whopping 32K, which was the most you could put inside the machine. There were folks who made bank-switched external memory modules, but they were very expensive.
Software Zen:
delete this;
