Floppy interface for ZX Spectrum
On 26. May 1998 schematic is slightly
modified, and now it works fine with Spectrum 128K. Instead of
connecting Spectrum's (Z80) address line A1 to FDC's pin 3 (A0) I
connected Spectrum's line A7.
It was necessary, because 128K models uses condition that A1 and A15 are low by IN/OUT for accessing memory bank control logic in ULA chip. Actually only conditions are: A1=0 and IORQ line of Z80 is active (low). Both IN and OUT instructions activates memory bank control port. A15 could not be controlled in most cases - by INI and OUTI it takes value from B register, which is used as loop counter.
I purchased Spectrum 128K before about 2 months, and this is first 128K model what I seen from close...
Port addresses are now:
Command/status register: #73
Track register: #F3
Sector register: #77
Data register: #F7
Joystick interface is Kempston
Port address is: #DF , you may use also more common address #1F.
Bits 6-7 of this port are used for read signals INTRQ and DRQ of FDC chip.