There is no official method of determining which model of Spectrum code is running on, however one method is to
look for differences in the ROM on the machine.
There were six official models of Spectrum released:
- 48K with a single rom (16K had the same ROM)
- 128K with 2 roms
- Spanish 128K released 1985
- +2 with a built-in Cassette Deck
-
+2A and +3 - These have the same roms just differ with the +3 having a built-in 3" floppy drive
instead of the cassette deck.
Below is a routine which will return a value representing the machine type the code is running on in the Accumulator.
It works by first paging out the 48K rom - something that will do nothing on a real 48K machine,
before checking for the Copyright string present in the 48K rom.
If that is not present it then attempts to page out the rom on a +2A/+3 machine - as they have 4 ROM's,
then checking for strings present on the +2A/+3, then the +2 and finally the Spanish 128K machine.
If it got this far without a match then it's running on an original UK 128K machine.
Rom selection
There's two additional routines in here, romSel1 and romSel2,
which handle the ROM selection and could be reused.
They both take the new value of the port which manages the rom selection in the Accumulator and updates both the
appropriate port and system variable.
For romSel1 load the Accumulator from 0x5BFC and make your changes before calling this routine.
For romSel2 load the Accumulator from 0x5B67 and make your changes before calling this routine.
machinetype.z80 source
; ***************************************************************************
; Determine which model of ZX Spectrum the code is running on.
;
; Author: Peter Mount, Area51.dev & Contributors
; URL: https://area51.dev/sinclair/asm/machinetype/
; ***************************************************************************
; The model's to detect
machine_48 = 0 ; Spectrum 48k
machine_128 = 1 ; Spectrum 128K UK
machine_128es = 2 ; Spectrum 128K Spanish
machine_plus2 = 3 ; Spectrum +2
machine_plus3 = 4 ; Spectrum +2A/+3
;
; detectMachine Detect the type of machine running this code
;
; Exit:
; A Model type
; Z Set for a 16K/48K machine, Reset for any 128K machine
;
detectMachine:
PUSH BC ; Save registers as BC is needed for ROM selection
PUSH DE ; and D for passing the result back
CALL detectMachine1 ; Call detection routine
LD A, D ; Copy result into A
POP DE ; Restore registers
POP BC
AND A ; CP 0 so Z is true for a 48K and NZ for any 128K machine
RET
detectMachine1:
LD A, (0x5B5C) ; Switch rom
PUSH AF ; Save current rom
AND &EF ; to ensure non-48k rom is selected, bit 4 is 0
CALL romSel1 ; change rom1, will do nothing on a 48K
CALL detectMachine2 ; run tests
POP AF ; Restore rom
; romSel1 Update rom selection port on 128K and later machines
;
; Entry:
; A New value of port, based on current value in 0x5BFC
;
; Exit:
; A undefined
; BC undefined
;
romSel1: LD BC, 0x7FFD ; Select rom on 128K and later
DI ; Switch the port between DI/EI
LD (0x5B5C), A
OUT (C), A
EI
RET
detectMachine2:
LD D, machine_48 ; Test for a 48K
LD A, (0x153B) ; Address of 1 in (C)1982 in spectrum 48k rom
CP '1'
RET Z
LD A, (0x5B67) ; Switch rom on +3
PUSH AF ; Save current rom
AND &FB ; This time bit 2 is 0 on second port, does nothing on 128/+2
CALL romSel2
CALL detectMachine3 ; run tests
POP AF ; restoring old rom
; romSel2 Update rom selection port on +2A and +3 machines
;
; Entry:
; A New value of port, based on current value in 0x5B67
;
; Exit:
; A undefined
; BC undefined
;
romSel2: LD BC, 0x1FFD ; Select rom on +2A/+3
DI ; Switch the port between DI/EI
LD (0x5B67), A
OUT (C), A
EI
RET
detectMachine3:
LD D, machine_plus3 ; Test for +3
LD A, (0x168e) ; Address of "SPECTRUM" in +3 rom 0
CP 'S'
RET Z
LD D, machine_plus2 ; Test for +2
LD A, (0x0562) ; See if we are a +2
CP '1' ; This is 1 in "(C)1982 Amstrad"
RET Z
LD D, machine_128es ; See if Spanish 128K
LD A, (0x0508)
CP '1' ; This is 1 in "(C) 1985 Sinclair"
RET Z
LD D, machine_128 ; We must be a 128K if we got here
RET