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.Z80 (Z80) [from Z80 documentation]The old .Z80 snapshot format (for version 1.45 and below) looks like this:Offset Length Description---------------------------0 1 A register1 1 F register2 2 BC register pair (LSB, i.e. C, first)4 2 HL register pair6 2 Program counter8 2 Stack pointer10 1 Interrupt register11 1 Refresh register (Bit 7 is not significant!)12 1 Bit 0 : Bit 7 of the R-registerBit 1-3: Border colourBit 4 : 1=Basic SamRom switched inBit 5 : 1=Block of data is compressedBit 6-7: No meaning13 2 DE register pair15 2 BC' register pair17 2 DE' register pair19 2 HL' register pair21 1 A' register22 1 F' register23 2 IY register (Again LSB first)25 2 IX register27 1 Interrupt flipflop, 0=DI, otherwise EI28 1 IFF2 (not particularly important...)29 1 Bit 0-1: Interrupt mode (0, 1 or 2)Bit 2 : 1=Issue 2 emulationBit 3 : 1=Double interrupt frequencyBit 4-5: 1=High video synchronisation3=Low video synchronisation0,2=NormalBit 6-7: 0=Cursor/Protek/AGF joystick1=Kempston joystick2=Sinclair 2 Left joystick (or userdefined, for version 3 .Z80 files)3=Sinclair 2 Right joystickBecause of compatibility, if byte 12 is 255, it has to be regarded as being 1.After this header block of 30 bytes the 48K bytes of Spectrum memory followsin a compressed format (if bit 5 of byte 12 is one). The compression methodis very simple: it replaces repetitions of at least five equal bytes by afour-byte code ED ED xx yy, which stands for "byte yy repeated xx times".Only sequences of length at least 5 are coded. The exception is sequencesconsisting of ED's; if they are encountered, even two ED's are encodedinto ED ED 02 ED. Finally, every byte directly following a single ED is nottaken into a block, for example ED 6*00 is not encoded into ED ED ED 06 00but into ED 00 ED ED 05 00. The block is terminated by an end marker,00 ED ED 00.That's the format of .Z80 files as used by versions up to 1.45. Startingfrom version 2.0, a different format is used, since from then on also 128Ksnapshots had to be supported. This new format is used for all snapshots,either 48K or 128K.Version 2.01 and 3.0 .Z80 files start with the same 30 byte header asold .Z80 files used. Bit 4 and 5 of the flag byte have no meaning anymore,and the program counter (byte 6 and 7) are zero to signal a version 2.01or version 3.0 snapshot file.After the first 30 bytes, the additional header follows:Offset Length Description---------------------------* 30 2 Length of additional header block (see below)* 32 2 Program counter* 34 1 Hardware mode (see below)* 35 1 If in SamRam mode, bitwise state of 74ls259.For example, bit 6=1 after an OUT 31,13 (=2*6+1)If in 128 mode, contains last OUT to 7ffd* 36 1 Contains 0FF if Interface I rom paged* 37 1 Bit 0: 1 if R register emulation onBit 1: 1 if LDIR emulation on* 38 1 Last OUT to fffd (soundchip register number)* 39 16 Contents of the sound chip registers55 2 Low T state counter57 1 Hi T state counter58 1 Flag byte used by Spectator (QL spec. emulator)Ignored by Z80 when loading, zero when saving59 1 0FF if MGT Rom paged60 1 0FF if Multiface Rom paged. Should always be 0.61 1 0FF if 0-8191 is ROM, 0 if RAM62 1 0FF if 8192-16383 is ROM, 0 if RAM63 10 5x keyboard mappings for user defined joystick73 10 5x ascii word: keys corresponding to mappings above83 1 MGT type: 0=Disciple+Epson,1=Disciple+HP,16=Plus D84 1 Disciple inhibit button status: 0=out, 0ff=in85 1 Disciple inhibit flag: 0=rom pageable, 0ff=notThe value of the word at position 30 is 23 for version 2.01 files, and 54 forversion 3.0 files. The starred fields are the ones that constitute theversion 2.01 header, and their interpretation has remained unchanged exceptfor byte 34:Value: Meaning in v2.01 Meaning in v3.0x--------------------------------------------------------0 48k 48k1 48k + If.1 48k + If.12 SamRam SamRam3 128k 48k + M.G.T.4 128k + If.1 128k5 - 128k + If.16 - 128k + M.G.T.The documenation for versions 3.00 to 3.02 of Z80 had the entries for 'SamRam'and '48k + M.G.T.' in the second column of the above table reversed; alsobytes 61 and 62 of the format were wrong up to version 3.04. (The snapsproduced by the older versions of Z80 still follow what is above; thedocumentation for the older versions is wrong).The hi T state counter counts up modulo 4. Just after the ULA generates itsonce-in-every-20-ms interrupt, it is 3, and is increased by one every 5emulated milliseconds. In these 1/200s intervals, the low T state countercounts down from 17471 to 0 (17726 in 128K modes), which make a total of69888 (70908) T states per frame.The 5 ASCII words (high byte always 0) at 73-82 are the keys correspondingto the joystick directions left, right, down (!), up (!), fire respectively.Shift, Symbol Shift, Enter and Space are denoted by [,],/,\ respectively.The ascii values are used only to display the joystick keys; the informationin the 5 keyboard mapping words determine which key is actually pressed (andshould correspond to the ascii values). The low byte is in the range 0-7 anddetermines the keyboard row. The high byte is a mask byte and determines thecolumn. Enter for example is stored as 0x0106 (row 6 and column 1) and 'g'as 0x1001 (row 1 and column 4).Byte 60 must be zero, because the contents of the Multiface RAM is not savedin the snapshot file. If the Multiface was paged when the snapshot was saved,the emulated program will most probably crash when loaded back.Bytes 61 and 62 are a function of the other flags, such as byte 34, 59,60 and 83.Hereafter a number of memory blocks follow, each containing the compresseddata of a 16K block. The compression is according to the old scheme, exceptfor the end-marker, which is now absent. The structure of a memory block is:Byte Length Description---------------------------0 2 Length of compressed data (without this 3-byte header)If length=0xffff, data is 16384 bytes long and not compressed2 1 Page number of block3 [0] DataThe pages are numbered, depending on the hardware mode, in the following way:Page In '48 mode In '128 mode In SamRam mode------------------------------------------------------0 48K rom rom (basic) 48K rom1 Interface I, Disciple or Plus D rom, according to setting2 - rom (reset) samram rom (basic)3 - page 0 samram rom (monitor,..)4 8000-bfff page 1 Normal 8000-bfff5 c000-ffff page 2 Normal c000-ffff6 - page 3 Shadow 8000-bfff7 - page 4 Shadow c000-ffff8 4000-7fff page 5 4000-7fff9 - page 6 -10 - page 7 -11 Multiface rom Multiface rom -In 48K mode, pages 4,5 and 8 are saved. In SamRam mode, pages 4 to 8 are saved.In '128 mode, all pages from 3 to 10 are saved. There is no end marker.Warajevo writes v2 .Z80 files, but with some extensions to deal with itsTimex 2068 emulation:Byte 34: 128 signifies Timex 2068 emulation is active.Byte 35: If Timex 2068 is active, last OUT to port 244.Byte 36: If Timex 2068 is active, last OUT to port 255.xzx has also made various extensions to the .Z80 format:The AY registers are always saved into .Z80 snapshots, independentof the emulated machine. Bit 2 of byte 37 being set signifies thatthis feature is in use.+3 snapshots: The hardware field is written as '7', and a 55th byteis added to the header, which stores the last byte output to #1FFD.This 55th byte is added to all snapshots, which causes many otheremulators to reject them. If you have this problem, SnapConv may beable to help. Also, some versions of xzx could write a value of 8 tohardware field, but this should also be treated as a +3.A hardware field of '9' signifies Pentagon emulation, whilst '10'signifies Scorpion emulation. The Pentagon snapshots are (to quotefrom xzx's ChangeLog) "pretty much the same as standard 128K ones",whilst those for the Scorpion consist of 16 RAM pages.