ZX Spectrum memory and ROM names

The explorer's Z80 disassembly of a Spectrum tape, snapshot or tape file writes a name in place of an address operand when the address is one of those below: call LD_BYTES instead of call $0556, ld a,(LAST_K) instead of ld a,($5C08). The decoder names every 16-bit operand that equals a name, including the value in a load such as ld bc,$5C00, so a number that merely equals an address can be named too. $0000 is left unnamed for that reason (ld hl,0 is common).

The names are those of the Logan and O'Hara Complete Spectrum ROM Disassembly as the SkoolKit project publishes it at skoolkid.github.io/rom/maps/all.html. A hyphen in a ROM name (LD-BYTES) is written as an underscore (LD_BYTES). The page was read through a summarising fetch tool, not saved or compared with a ROM image, so the addresses are as that tool reported them. Only the routines the listing titles are named; labels inside a routine (such as PRINT-A-2) are not. The 174 ROM names are in the viewer's table; the entry points most often called from game code and loaders are below.

Memory map (48K)

Range	Name	What is there
`$0000`–`$3FFF`	ROM	The BASIC ROM (on the 128K machines one of two, chosen by port `$7FFD` bit 4).
`$4000`–`$57FF`	Screen bitmap	6144 bytes, see below.
`$5800`–`$5AFF`	Screen attributes	768 bytes, one per 8 by 8 cell.
`$5B00`–`$5BFF`	Printer buffer	256 bytes.
`$5C00`–`$5CB5`	System variables	The ROM's working storage, listed below.
`$5CB6`–`$FFFF`	Channels, BASIC program, variables, free RAM	RAMTOP (`$5CB2`) marks the upper end of what BASIC uses.

Screen layout

The display file at $4000 is 192 pixel rows of 32 bytes, one bit per pixel with bit 7 leftmost, but the rows are not in order. A pixel row y written as the bits y7 y6 y5 y4 y3 y2 y1 y0 starts at $4000 + (y7 y6) × $800 + (y2 y1 y0) × $100 + (y5 y4 y3) × $20: the screen is in three thirds, and inside a third the eight pixel rows of one character come $100 apart. The attribute file at $5800 is 24 rows of 32 bytes: bits 0 to 2 ink, bits 3 to 5 paper, bit 6 bright, bit 7 flash. The colours 0 to 7 are black, blue, red, magenta, green, cyan, yellow and white; bright brightens the seven colours and leaves black black. The border colour is port $FE bits 0 to 2. The viewer draws the colours at levels 0 and 215 (255 when bright), the usual emulator values, not a measurement.

System variables

Address	Name	Bytes
`$5C00`	KSTATE	8
`$5C08`	LAST_K	1
`$5C09`	REPDEL	1
`$5C0A`	REPPER	1
`$5C0B`	DEFADD	2
`$5C0D`	K_DATA	1
`$5C0E`	TVDATA	2
`$5C10`	STRMS	38
`$5C36`	CHARS	2
`$5C38`	RASP	1
`$5C39`	PIP	1
`$5C3A`	ERR_NR	1
`$5C3B`	FLAGS	1
`$5C3C`	TV_FLAG	1
`$5C3D`	ERR_SP	2
`$5C3F`	LIST_SP	2
`$5C41`	MODE	1
`$5C42`	NEWPPC	2
`$5C44`	NSPPC	1
`$5C45`	PPC	2
`$5C47`	SUBPPC	1
`$5C48`	BORDCR	1
`$5C49`	E_PPC	2
`$5C4B`	VARS	2
`$5C4D`	DEST	2
`$5C4F`	CHANS	2
`$5C51`	CURCHL	2
`$5C53`	PROG	2
`$5C55`	NXTLIN	2
`$5C57`	DATADD	2
`$5C59`	E_LINE	2
`$5C5B`	K_CUR	2
`$5C5D`	CH_ADD	2
`$5C5F`	X_PTR	2
`$5C61`	WORKSP	2
`$5C63`	STKBOT	2
`$5C65`	STKEND	2
`$5C67`	BREG	1
`$5C68`	MEM	2
`$5C6A`	FLAGS2	1
`$5C6B`	DF_SZ	1
`$5C6C`	S_TOP	2
`$5C6E`	OLDPPC	2
`$5C70`	OSPCC	1
`$5C71`	FLAGX	1
`$5C72`	STRLEN	2
`$5C74`	T_ADDR	2
`$5C76`	SEED	2
`$5C78`	FRAMES	3
`$5C7B`	UDG	2
`$5C7D`	COORDS	2
`$5C7F`	P_POSN	1
`$5C80`	PR_CC	2
`$5C82`	ECHO_E	2
`$5C84`	DF_CC	2
`$5C86`	DF_CCL	2
`$5C88`	S_POSN	2
`$5C8A`	S_POSNL	2
`$5C8C`	SCR_CT	1
`$5C8D`	ATTR_P	1
`$5C8E`	MASK_P	1
`$5C8F`	ATTR_T	1
`$5C90`	MASK_T	1
`$5C91`	P_FLAG	1
`$5C92`	MEMBOT	30
`$5CB0`	NMIADD	2
`$5CB2`	RAMTOP	2
`$5CB4`	P_RAMT	2

Sizes are the gaps between the addresses on the source page. Only the first address of a multi-byte variable is named: FRAMES+1 is shown as a plain number.

ROM entry points

Address	Name	Title in the ROM listing
`$0008`	ERROR_1	The 'error' restart
`$0010`	PRINT_A_1	The 'print a character' restart
`$0018`	GET_CHAR	The 'collect character' restart
`$0020`	NEXT_CHAR	The 'collect next character' restart
`$0028`	FP_CALC	The 'calculator' restart
`$0030`	BC_SPACES	The 'make BC spaces' restart
`$0038`	MASK_INT	The 'maskable interrupt' routine
`$0066`	RESET	The 'non-maskable interrupt' routine
`$028E`	KEY_SCAN	The 'keyboard scanning' subroutine
`$03B5`	BEEPER	The 'beeper' subroutine
`$04C2`	SA_BYTES	The 'SA-BYTES' subroutine
`$0556`	LD_BYTES	The 'LD-BYTES' subroutine
`$0D6B`	CLS	The 'CLS' command routine
`$0DAF`	CL_ALL	The 'clearing the whole display area' subroutine
`$11B7`	NEW	The 'NEW' command routine
`$1601`	CHAN_OPEN	The 'CHAN-OPEN' subroutine
`$2294`	BORDER	The 'BORDER' command routine
`$22AA`	PIXEL_ADDR	The 'pixel address' subroutine
`$22DC`	PLOT	The 'PLOT' command routine
`$2D2B`	STACK_BC	The 'STACK-BC' subroutine
`$3D00`	CHAR_SET	Character set (the 96 character patterns; `CHARS` holds this address minus 256)

Not described

The labels inside routines, the ROM's data tables beyond the start addresses, the 128K and +3 ROMs, and what each routine takes and returns. The names were not compared with a ROM image.

.TAP File Format – Memory and ROM names

Memory map (48K)

Screen layout

System variables

ROM entry points

Not described

Links

Reference