2020-01-26 06:42:03 +11:00
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# TRS-80 Model 4p
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## Ports
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Address Read Write
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FC-FF Cassette in Cassette out, resets
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F8-FB Rd printer status Wr to printer
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F4-F7 - Drive select
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F3 FDC data reg FDC data reg
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F2 FDC sector reg FDC sector reg
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F1 FDC track reg FDC track reg
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F0 FDC status reg FDC cmd reg
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EC-EF Reset RTC INT Mode output
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EB RS232 recv holding reg RS232 xmit holding reg
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EA UART status reg UART/modem control
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E9 - Baud rate register
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E8 Modem status Master reset/enable
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UART control reg
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E4-E7 Rd NMI status Wr NMI mask reg
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E0-E3 Rd INT status Wr INT mask reg
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CF HD status HD cmd
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CE HD size/drv/hd HD size/drv/hd
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CD HD cylinder high HD cylinder high
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CC HD cylinder low HD cylinder low
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CB HD sector # HD sector #
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CA HD sector cnt HD sector cnt
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C9 HD error reg HD write precomp
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C8 HD data reg HD data reg
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C7 HD CTC chan 3 HD CTC chan 3
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C6 HD CTC chan 2 HD CTC chan 2
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C5 HD CTC chan 1 HD CTC chan 1
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C4 HD CTC chan 0 HD CTC chan 0
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C2-C3 HD device ID -
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C1 HD control reg HD Control reg
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C0 HD wr prot reg -
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94-9F - -
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90-93 - Sound option
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8C-8F Graphic sel 2 Graphic sel 2
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8B CRTC Data reg CRTC Data reg
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8A CRTC Control reg CRTC Control reg
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89 CRTC Data reg CRTC Data reg
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88 CRTC Control reg CRTC Control reg
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84-87 - Options reg
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83 - Graphic X reg
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82 - Graphic Y reg
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81 Graphics RAM Graphics RAM
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80 - Graphics options reg
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Bit map
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Address D7 D6 D5 D4 D3 D2 D1 D0
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F8-FB-Rd Busy Paper Select Fault - - - -
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EC-EF-Rd (any read causes reset of RTC interrupt)
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EC-EF-Wr - CPU - Enable Enable Mode Cass -
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Fast EX I/O Altset Select Mot on
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E0-E3-Rd - Recv Recv Xmit 10 Bus RTC C Fall C Rise
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Error Data Empty int Int Int Int
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E0-E3-Wr - Enable Enable En.Xmit Enable Enable Enable Enable
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Rec err Rec dat Emp 10 int RTC int CF int CR int
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90-93-Wr - - - - - - - Sound
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Bit
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84-87-Wr Page Fix upr Memory Memory Invert 80/64 Select Select
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mem bit 1 bit 0 video Bit 1 Bit 0
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2020-02-11 03:25:05 +11:00
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## System memory map
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2020-01-26 06:42:03 +11:00
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### Memory map 1 - model III mode
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0000-1fff ROM A (8K)
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2000-2fff ROM B (4K)
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3000-37ff ROM C (2K) - less 37e8/37e9
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37e8-37e9 Printer Status Port
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3800-3bff Keyboard
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3c00-3fff Video RAM (page bit selects 1K or 2K)
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4000-7fff RAM (16K system)
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4000-ffff RAM (64K system)
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### Memory map 2
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0000-37ff RAM (14K)
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3800-3bff Keyboard
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3c00-3fff Video RAM
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4000-7fff RAM (16K) end of one 32K bank
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8000-ffff RAM (32K) second 32K bank
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### Memory map 3
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0000-7fff RAM (32K) bank 1
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8000-f3ff RAM (29K) bank 2
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f400-f7ff Keyboard
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f800-ffff Video RAM
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### Memory map 4
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0000-7fff RAM (32K) bank 1
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8000-ffff RAM (32K) bank 2
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2020-02-11 03:25:05 +11:00
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## TRSDOS memory map
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0000-25ff Reserved for TRSDOS operations
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2600-2fff Overlay area
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3000-HIGH Free to use
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HIGH-ffff Drivers, filters, etc
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Use `MEMORY` command to know value of `HIGH`
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2020-01-26 06:42:03 +11:00
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## Supervisor calls
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SVC are made by loading the correct SVC number in A, other params in other regs,
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and then call `rst 0x28`.
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Z is pretty much always used for success or as a boolean indicator. It is
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sometimes not specified when there's not enough tabular space, but it's there.
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When `-` is specified, it means that the routine either never returns or is
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always successful.
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Num Name Args Res Desc
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00 IPL - - Reboot the system
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01 KEY - AZ Scan *KI, wait for char
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02 DSP C=char AZ Display character
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03 GET DE=F/DCB AZ Get one byte from device or file
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04 PUT DE=F/DCB C=char AZ Write one byte to device or file
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05 CTL DE=DBC C=func CAZ Output a control byte
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06 PRT C=char AZ Send character to printer
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07 WHERE - HL Locate origin of SVC
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08 KBD - AZ Scan keyboard and return
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09 KEYIN HL=buf b=len c=0 HLBZ Accept a line of input
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0a DSPLY HL=str AZ Display message line
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0b LOGER HL=str AZ Issue log message
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0c LOGOT HL=str AZ Display and log message
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0d MSG DE=F/DCB HL=str AZ Send message to device
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0e PRINT HL=str AZ Print message line
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0f VDCTL special spc Video functions
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10 PAUSE BC=delay - Suspend program execution
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11 PARAM DE=ptbl HL=str Z Parse parameter string
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12 DATE HL=recvbuf HLDE Get date
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13 TIME HL=recvbuf HLDE Get time
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14 CHNIO IX=DCB B=dir C=char - Pass control to next module in device chain
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15 ABORT - - Abort Program
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16 EXIT HL=retcode - Exit to TRSDOS
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18 CMNDI HL=cmd - Exec Cmd w/ return to system
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19 CMNDR HL=cmd HL Exec Cmd
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1a ERROR C=errno - Entry to post an error message
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1b DEBUG - - Enter DEBUG
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1c CKTSK C=slot Z Check if task slot in use
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1d ADTSK C=slot - Remove interrupt level task
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1e RMTSK DE=TCB C=slot - Add an interrupt level task
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1f RPTSK - - Replace task vector
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20 KLTSK - - Remove currently executing task
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21 CKDRV C=drvno Z Check drive
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22 DODIR C=drvno b=func ZBHL Do directory display/buffer
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23 RAMDIR HL=buf B=dno C=func AZ Get directory record or free space
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28 DCSTAT C=drvno Z Test if drive assigned in DCT
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29 SLCT C=drvno AZ Select a new drive
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2a DCINIT C=drvno AZ Initialize the FDC
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2b DCRES C=drvno AZ Reset the FDC
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2c RSTOR C=drvno AZ Issue a FDC RESTORE command
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2d STEPI C=drvno AZ Issue a FDC STEP IN command
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2e SEEK C=drvno DE=addr - Seek a cylinder
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2f RSLCT C=drvno - Test for drive busy
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30 RDHDR HL=buf DCE=addr AZ Read a sector header
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31 RDSEC HL=buf DCE=addr AZ Read a sector
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32 VRSEC DCE=addr AZ Verify sector
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33 RDTRK HL=buf DCE=addr AZ Read a track
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34 HDFMT C=drvno AZ Hard disk format
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35 WRSEC HL=buf DCE=addr AZ Write a sector
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36 WRSSC HL=buf DCE=addr AZ Write system sector
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37 WRTRK HL=buf DCE=addr AZ Write a track
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38 RENAM DE=FCB HL=str AZ Rename file
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39 REMOV DE=D/FCB AZ Remove file or device
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3a INIT HL=buf DE=FCB B=LRL AZ Open or initialize file
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3b OPEN HL=buf DE=FCB B=LRL AZ Open existing file or device
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3c CLOSE DE=FCB/DCB AZ Close a file or device
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3d BKSP DE=FCB AZ Backspace one logical record
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3e CKEOF DE=FCB AZ Check for EOF
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3f LOC DE=FCB BCAZ Calculate current logical record number
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40 LOF DE=FCB BCAZ Calculate the EOF logical record number
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41 PEOF DE=FCB AZ Position to end of file
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42 POSN DE=FCB BC=LRN AZ Position file
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43 READ DE=FCB HL=ptr AZ Read a record
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44 REW DE=FCB AZ Rewind file to beginning
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45 RREAD DE=FCB AZ Reread sector
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46 RWRIT DE=FCB AZ Rewrite sector
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47 SEEKSC DE=FCB - Seek cylinder and sector of record
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48 SKIP DE=FCB AZ Skip a record
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49 VER DE=FCB HLAZ Write and verify a record
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4a WEOF DE=FCB AZ Write end of file
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4b WRITE DE=FCB HL=ptr AZ Write a record
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4c LOAD DE=FCB HLAZ Load program file
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4d RUN DE=FCB HLAZ Run program file
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4e FSPEC HL=buf DE=F/DCB HLDE Assign file or device specification
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4f FEXT DE=FCB HL=str - Set up default file extension
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50 FNAME DE=buf B=DEC C=drv AZHL Get filename
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51 GTDCT C=drvno IY Get drive code table address
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52 GTDCB DE=devname HLAZ Get device control block address
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53 GTMOD DE=modname HLDE Get memory module address
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55 RDSSC HL=buf DCE=addr AZ Read system sector
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57 DIRRD B=dirent C=drvno HLAZ Directory record read
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58 DIRWR B=dirent C=drvno HLAZ Directory record write
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5a MUL8 C*E A Multiply C by E
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5b MUL16 HL*C HLA Multiply HL by C
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5d DIV8 E/C AE Divides E by C
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5e DIV16 HL/C HLA Divides HL by C
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60 DECHEX HL=str BCHL Convert Decimal ASCII to binary
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61 HEXDEC HL=num DE=buf DE Convert binary to decimal ASCII
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62 HEX8 C=num HL=buf HL Convert 1 byte to hex ASCII
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53 HEX16 DE=num HL=buf HL Convert 2 bytes to hex ASCII
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64 HIGH$ B=H/L HL=get/set HLAZ Get or Set HIGH$/LOW$
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65 FLAGS - IY Point IY to system flag table
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66 BANK B=func C=bank BZ Memory bank use
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67 BREAK HL=vector HL Set Break vector
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68 SOUND B=func - Sound generation
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2020-02-22 02:39:51 +11:00
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## Personal reverse engineering
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This section below contains notes about my personal reverse engineering efforts.
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I'm not an expert in this, and also, I might not be aware of existing, better
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documentation making this information useless.
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### Bootable disk
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I'm wondering what makes a disk bootable to the TRS-80 and how it boots it.
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When I read the raw contents of the first sector of the first cylinder of the
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TRS-DOS disk, I see that, except for the 3 first bytes (`00fe14`), the rest of
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the contents is exactly the same as what is at memory offset `0x0203`, which
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seems to indicates that the bootloader simply loads that contents to memory,
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leaving the first 3 bytes of RAM to either random contents or some predefined
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value (I have `f8f800`).
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A non-bootable disk starts with `00fe14`, but we can see the message "Cannot
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boot, DA TA DISK!" at offset `0x2a`.
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I'm not sure what `00fe14` can mean. Disassembled, it's
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`nop \ rst 0x28 \ ld b, c`. It makes sense that booting would start with a
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service call with parameters set by the bootloader (so we don't know what that
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service call actually is), but I'm not sure it's what happens.
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I don't see any reference to the `0x2a` offset in the data from the first
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sector, but anyways, booting with the non-bootable disk doesn't actually prints
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the aformentioned message, so it might be a wild goose chase.
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In any case, making a disk bootable isn't a concern as long as Collapse OS uses
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the TRS-DOS drivers.
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