Hello, is it possible to use io on a z80 to select different memory chips. Something like bankswitching, using an out command to select a memory chip? Greetings Frank
z80 memory io selection
Started by ●February 7, 2008
Reply by ●February 7, 20082008-02-07
Frank Eggink wrote:> is it possible to use io on a z80 to select different memory chips. > Something like bankswitching, using an out command to select a memory chip? >Whyever not? But why are you using a Z80, are you an antique dealer?
Reply by ●February 7, 20082008-02-07
No not an antique dealer. Just trying to build some z80 system to learn and for fun. But how can it be done? using io to select memory chips. Gr.. Frank "Paul Burke" <paul@scazon.com> wrote in message news:610driF1sj0oaU1@mid.individual.net...> Frank Eggink wrote: > >> is it possible to use io on a z80 to select different memory chips. >> Something like bankswitching, using an out command to select a memory >> chip? >> > > Whyever not? But why are you using a Z80, are you an antique dealer?
Reply by ●February 7, 20082008-02-07
Frank Eggink wrote:>>> is it possible to use io on a z80 to select different memory chips. >>> Something like bankswitching, using an out command to select a memory >>> chip? >>> >> Whyever not? But why are you using a Z80, are you an antique dealer? >> No not an antique dealer. > Just trying to build some z80 system to learn and for fun. > But how can it be done? using io to select memory chips. The Z80 supports 64K memory without bank switching. That should be enough for learning and having fun. If you need more, pick a CPU with a wider address bus.
Reply by ●February 7, 20082008-02-07
On 2008-02-07, Frank Eggink <freggink@gmx.net> wrote:> > is it possible to use io on a z80 to select different memory chips. > Something like bankswitching, using an out command to select a memory chip?Many of the later Z80 micros did this. The Amstrad PCW and Cambridge Z88 both did for instance. I've found schematics for the PCW at http://www.caliban.org/pcw_home.html if you are interested in a little reverse engineering. -- Andrew Smallshaw andrews@sdf.lonestar.org
Reply by ●February 7, 20082008-02-07
On Feb 7, 2:53=A0pm, "Frank Eggink" <fregg...@gmx.net> wrote:> Hello, > > is it possible to use io on a z80 to select different memory chips. > Something like bankswitching, using an out command to select a memory chip=?> > Greetings > > FrankHi Frank, decode /IORQ for the chip select ld BC,address in a,(c) out (c),a This gives full 64k mapping for the ioMemory. Rocky
Reply by ●February 7, 20082008-02-07
> is it possible to use io on a z80 to select different memory chips. > Something like bankswitching, using an out command to select a memory > chip?You betcha. (You mean that chip hasn't died yet?) JJS
Reply by ●February 7, 20082008-02-07
> No not an antique dealer.Then you're an antique reproductionist.> Just trying to build some z80 system to learn and for fun. > But how can it be done? using io to select memory chips.Remembering back to my hobbyist use of the "Timex Sinclair ZX80" in 1982, It's very easy to do what you want. (Warning: 25 year old memory is not accurate.) Referring to your Z80 manual, you'll see that when you call the OUT instruction you trigger an I/O pulse plus the A register on the data bus. Latch the data bus data onto an 273 type latch using the I/O pulse. Use the latched data for bank switching. I have a memory that the B register is also placed on the address bus so you can use that for additional addressing. This will only work with SRAM because you will turn off DRAM refreshing capability if you switch out DRAM. JJS
Reply by ●February 7, 20082008-02-07
Andrew Smallshaw wrote:> On 2008-02-07, Frank Eggink <freggink@gmx.net> wrote: > >>is it possible to use io on a z80 to select different memory chips. >>Something like bankswitching, using an out command to select a memory chip? > > > Many of the later Z80 micros did this. The Amstrad PCW and Cambridge > Z88 both did for instance. I've found schematics for the PCW at > http://www.caliban.org/pcw_home.html if you are interested in a > little reverse engineering. >I have lost my schematics for the Coleco Adam, which bank switched the Z80 for 128kB RAM and mapped ROMs. The AdamNet bus was token passing; the entire design was quite interesting. Anyone have the schematics? Michael
Reply by ●February 7, 20082008-02-07
Frank Eggink wrote:> Hello, > > is it possible to use io on a z80 to select different memory chips. > Something like bankswitching, using an out command to select a memory chip?I built a 128kb Z80 back in 1982. I added a second bank of 64kb dram and used a page register to map 16kb pages in and out of the top 16kb physical memory. Putting an interrupt routine up there will definitely fsk you up (: