tdg8934 wrote: ↑
Fri Jul 05, 2019 4:31 pm
I'm beginning to think this post should be brought into the Spectrum section but its ok with me either way.
So is the Spectrum just a supped up ZX81 with better graphics, sound, etc. Is the expansion port the same on both. (i.e. can a ZXPand+ be used on a Spectrum or TS2068 or other related system? Many companies go with what they know and modify their product for the next version 2.0 - if you get what I mean. I'm wondering about the commonalities between them or are they completely new designs both just having to be run off of a Z80 processor.
I’ll move the thread if that is what is wanted...
The ZX Spectrum is a development which greatly expands on the ZX81. So I would classify as a new machine rather than a souped-up ZX81.
ZX81 vs. ZX Spectrum (all the following assume off the shelf standard machines)
RAM 1K bytes vs. 16K bytes or 48K bytes
ROM 8K bytes vs. 16K bytes with a greatly expanded BASIC with keywords to control the graphics, colour and sound
Minimal hardware for the display system that needs to use the CPU vs. Special custom system that includes “high resolution” pixel graphics and colour that runs independently of the CPU
Special character set vs. ASCII character set
No sound vs. Bleeper sound
So in terms of hardware, the only common things are: the same Z80 CPU (but clocked at slightly different speeds), a similar memory map layout, a similar keyboard matrix. Both use a ULA, but the functionality is very different (you can remove the CPU from a Spectrum and you will still get a display on the TV screen, it will be a multicoloured mess of different coloured and flashing pixels, but it will be there). Everything else is different.
The expansion edge-connector port is different on a ZX81 compared to a ZX Spectrum. Only a very limited number of expansion or I/O devices are compatible with both machines. For example the ZX Printer (and any compatible printer) and some Kempston joystick interfaces.
A memory expansion can only be used on a 16K byte ZX Spectrum and has to have it’s RAM decoded to 0x8000 to 0xFFFF.
No memory expansions can be used with other ZX Spectrum models.
The Z80 memory controls signals on the expansion edge-connector are in a different place. And there is no control signal to disable any of the internal RAM. So ZX81 RAM packs and the ZXpand won’t work, even on a 16K machine.
The expansion edge-connector on the TS2068 is more similar to the ZX81 than on the ZX Spectrum.
In terms of the BASIC, at the user level, apart from keywords like SCROLL, SLOW, FAST etc, ZX81 programs will work on a ZX Spectrum if typed in. But the ZX Spectrum tape system cannot load ZX81 programs from tape.
Although the ZX Spectrum ROM code has some sections that are similar to the code in the ZX81 ROM, a lot of it is new code.
There are a number of competing modern mass storage interfaces for the ZX Spectrum, including FDD, HDD, CF and SD card solutions. There is also some that allow a network connection.