Zx81 Memory Map, If this is present then, as well as the standard 16K memory map, there are three other modes available. The memory detection procedure in both ZX80 and ZX81 BIOS stops after 16 KBytes (at 8000h), and initializes the stack pointer at that address, even if more memory is installed. ZX81 memory test program. A huge number of expansion RAM packs were produced for the Sinclair computers. Vintage Computers All times are GMT. The result is a fun, compressed map that runs. The time now is 9:09 pm. The RAM chip Data and Address connections match 26 the connections as they are on the ZX81. This had to be connected to the expansion port on the back of the computer. The ZX81 was designed to minimize the number of parts needed, so the memory layout reflects that design descision. The ROM shows up in 4 locations, and the RAM is mirrored too. Decimal Hex Memory map as designed, where current peripherals fit in the map and suggestions about standardization. Sinclair ZX81 Overview The Sinclair ZX81 is my first computer, in 1982 (kit). The digression about memory addresses interrupted our examination of the memory map before we had considered the final four areas. Since this document is more about software than hardware, I won't go into the hardware decisions that created the memory layout. Manual for ZX 81 Sinclair computer. Exactly on these issues the Giant is a great solution: it offers RAM, EPROM as well as EEPROM areas. They are all documented in the user manual but in summary they are: RAM from 0x2000 (8192 dec) to 0x9FFF (40959 dec) – useful for HRG (high resolution The memory map on a ZX81 is a ZX81 is interesting. The Character Map Below are the visible characters Sep 28, 2025 ยท I adapted a blocky world map program to the ZX81, working around its missing DATA command. 95 in kit). Other very popular computers were the Commodore 64 and the Apple II but were far more expensive (ZX81 was ten times cheaper than Apple II Plus). Posts about ZX81 written by Charles The vLA81 has a few ‘hidden’ features which can only be fully unlocked with a 32K memory upgrade. The next 128 or so bytes are used to store system variables, and this is followed by screen memory. For many, that was enough. The ZX81 is a very simple computer and only has 1KB of memory, which could be expanded to 16KB by using a RAMpack. To resume, the calculator stack is an area of memory that the ZX81 uses to store any temporary results generated while it is doing arithmetic. . ZX81-Internal-16K-Expansion 'No Wobbly Edition' This little PCB is a 'quick and dirty, no wobbly' 16K internal memory expansion for the Sinclair ZX81. There are many memory expansion possibilities for the ZX81, however the ZX81 Giant board is something completely new: up to 144 kB of memory! The important question is always where, how much and what kind of memory is needed. Coding Examples. Z80 Assembly programming for the ZX81! The Keyboard Layout Reading the keyboard We can read in a row of the keyboard by setting BC to the correct value and using IN A, (C) the resulting byte will contain a 0 if the key is pressed, 1 if it is not. They are all documented in the user manual but in summary they are: RAM from 0x2000 (8192 dec) to 0x9FFF (40959 dec) – useful for HRG (high resolution A14' /RAMCS /ROMOE CPUCLK /NMI OLD_SYNC /HALT A15' [D7] ULA_PIN20 The program starts from 16640 because the first 16 K (locations 0-16383) of the ZX81's memory map is the 8 K ROM plus a copy of the 8 K ROM. Here is the memory map of the ZX81 (assuming the ZX81 has 16K of memory). Therefor the memory map looks like this; As I understand it, Only the 8 ROM from 0x000 to 0x1FFF and the 16k RAM from 0x4000 to 0x7FFF actually matter. They do not match the Datasheet pinouts of the respective RAM /BUSRQ 25 chips. Sinclair and Timex offered 16K RAM units for the ZX80, ZX81 and TS 1000 computers. It is one of those home computers very popular in the '80s and affordable (£49. A13 is the only line used to decode if ROM or RAM is accessed. Technical info, memory map, instruction set. RAM Memory Expansion While resourceful owners could accomplish a lot with the 1K or 2K of RAM built in to their computers, more serious uses required more RAM. s7lpq, ukbn3h, trebg, b8m7, maz7t, no, wvg, yi, 7g0psvg, ddps,
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