LDOS 5.3.1 for the Model III - FED/CMD Disassembled

FED/CMD

Other Navigation

LDOS 5.3.1 FED/CMD Disassembly - The File Editor (Model III)

FED/CMD, the LDOS File Editor (its title reads FED - File Editor Version 1.0.2, Copyright 1987 MISOSYS), displays and changes the records of a file one at a time: FED (filespec) (M-40-060, version 5). The record of 256 bytes is read into an edit buffer and shown in hex and as characters, either all 256 bytes (the 256 byte mode, with the inputs in a box at the right edge) or a window of 128 bytes with more room for the labels (the 128 byte mode). One letter is a command: the semicolon and the minus sign step through the records, B, E and R position, H and A change bytes in hex or as characters, S writes the record back, C, F, G, L, Z and M search the file or its load module structure, D, P and O print, T switches the display and = shows a byte in binary; ENTER alone shows the list of the commands. FED works on the file through @POSN, @READ and @VER and never closes it.

The file is a load module of 6918 bytes: a copyright record, then thirty load blocks for 59A8H-5BDBH, 5C0EH-6030H, 6063H-68F8H and 68FEH-746BH (6747 bytes) and the transfer address record for 6063H. The texts and a whole help screen of 1024 bytes come first, then the cells, then the code. Every buffer is below the file, from 5200H: the file control block 5242H, the edit buffer 5262H, the buffer of the file 5362H, a copy 5462H and the image of the screen 5562H, which is built in memory and copied to video memory. One file serves the Model I and the Model III: the start-up picks the address of the BREAK switch of LDOS by the ROM and puts a RET there, so that BREAK comes to FED as a key.

What FED Does

About This Page

5200H - The Work Areas Below the File

FED/CMD loads from 59A8H, so the memory from 5200H, where LDOS loads a command, up to 59A7H is free. FED uses it for the saved input box, the file control block, the edit buffer, the buffer of the file, the copy taken for a search, the image of the screen and the command line. None of these bytes is in the file.

59A8H - The Texts of the Screen

The first load block starts with the texts of the screens. 59A8H-59C7H are the digit pairs of the row and column labels, 59C8H-59D5H the name of the file as shown, then the title, the copyright, the labels and the error texts. A text displayed by 65E5H ends at the byte with bit 7 set, whose bit 7 is cleared on the screen.

5C0EH - The Help Screen

The load blocks from 5C0EH to 600DH hold a whole screen, 16 rows of 64 characters: the list of the commands. The key ENTER alone at the command line (6235H) swaps these 1024 bytes with video memory (6E96H), blinks ENTER on the last row until ENTER is pressed and swaps them back.

600EH - The Cells of FED

The variables of FED/CMD, all 00H in the file but 601BH. The search string and the address of L follow beyond the load block, at 6031H-6062H.

6063H - The Start: the BREAK Switch and the File

LDOS Ready loads FED/CMD at 59A8H-746BH and jumps to 6063H, the transfer address, with Register Pair HL at the rest of the command line. The command is FED (filespec): with a file specification FED opens it at once, else it shows its title and asks for one. 6064H tells the Model III from the Model I by the ROM byte 0125H and finds the BREAK switch of LDOS, which gets a RET while FED runs, so that the BREAK key reaches FED as key 01H. 657CH makes the texts capitals when the video has no lower case.

60ADH - The Command Loop

Every command ends by a jump to 60ADH. The stack is set again at 41E0H, the cursors blink, and the key from the ROM's keyboard scan is taken. The state at 6013H says what a key means: 00H, a new command (61C6H); 01H and 02H, a digit of H; 03H, a character of A; 08H-0AH, the ENTER after S, N or X. The four arrow keys and SHIFT UP ARROW move the cursor in every state but A. The other states collect the characters typed after R, L, C, F, D or P until ENTER or the last place.

610CH - The Characters After a Command

The characters typed after R (four hex digits), L (four), F (hex digits) and C (any characters) go to the command line through 6791H, each shown at the cursor, which moves down the input box in the 256 byte mode and to the right in the 128 byte mode. The state is counted up by each character; when the last place is reached, or on ENTER, the command is carried out. ENTER is stored as 0DH at the end of what was typed.

616AH - Carry Out the Command

The line typed is ended by 0DH; the state picks the routine: bit 6 F (702BH), bit 7 C (7073H), bit 4 L (61A9H), else R. R reads the four hex digits after the letter, refuses a number beyond the last record with an asterisk in the command line, and shows the record.

61A9H - L: The Address to Locate

After the fourth hex digit of L (or ENTER), the input box is drawn five rows high and what is under it is kept; the address is taken into 6031H, 6030H is set to FFH, the search kind of L, and the search starts from record 0 at 7174H.

61C6H - The Command Letters

With no command under way, the key in Register B picks the command: the letter is shown in the command line (5962H and at the cursor, 67BCH), and the commands that take more keys set their state at 6013H. ENTER alone shows the help screen; any other key goes to 65FFH, which moves the cursor for the arrow keys and ignores the rest.

624EH - =: The Byte in Binary

The equals sign works in the 128 byte mode only: the input line at 3FCAH gets X'hh'= (the hex digits kept at 5B68H by 6679H), then the eight bits of the byte at the cursor as 0 and 1, with a comma after the fourth. The byte is rotated eight times, so it is the same at the end.

6284H - Forward, Backward, R, B and E

The semicolon shows the next record and the minus sign the one before, unless the last or the first is shown; the cursor keeps its place in the record. R takes four hex digits in the input box. B shows record 0 with the cursor on byte 00H; E shows the last record with the cursor on the last byte of the file, by the end of file byte of the file control block.

62F9H - N, D, P, O and T

N waits for ENTER and then asks for a new file. D prints the records from the one shown to the end, three to a page; P prints the edit buffer between two blank lines; O sends a top of form. Each checks the printer first (6F9BH). T switches the display mode and builds the screen again.

63A6H - S: Save the Record

S waits for ENTER; then the edit buffer is copied into the buffer of the file, the file is positioned to the record shown and the record is written with @VER (write and read back). For DIR/SYS, the directory entry code 01H at 5249H, the operand of SYS0's WRSECT is set for the time of the write to WRPROT's 0EH, so that the sector gets the deleted data mark every directory sector has; the read back then gives error 06H, which is the good end here.

6409H - X, F, C, L and G

X waits for ENTER and then ends FED. F (hex digits) and C (characters) open an input box of seven rows (the input line in the 128 byte mode) for the string; L opens one of five rows for the address. G repeats the last search: from the byte after the cursor for a string, from the block after the found address for L, or shows an asterisk when there was none.

6466H - Z: The Next Load Block

With the cursor on a type byte (01H, 05H, 07H, 10H or 1FH) of a load module, Z skips its block by its length byte and puts the cursor on the next type byte, reading the records it passes into. A type byte 02H, the transfer address, ends the zip with an asterisk; any other byte gives Cursor not on Type byte.

64CEH - A Spare Area

128 bytes of 00H in the file between the commands and the routines. No instruction of FED/CMD reads or writes them.

654EH - Clear the Screen; the Register Saver

654EH fills video memory 3C00H-3FFFH with spaces. Many routines start with CALL 655FH: it takes the rest of the routine as a subroutine, after saving Register Pairs HL, DE, BC, AF, IX and IY, and gives them all back when the routine returns, so the caller finds every register as it was.

657CH - Lower Case or Capitals

A machine without the lower case kit shows a lower case letter as another character, so FED tries a lower case a (61H) at 3C00H: if it reads back, the video has lower case; else every lower case letter of the texts 59A8H-600DH (including the help screen) is made a capital, keeping bit 7 of the bytes that end a text.

65B0H - The Name of the File as Shown

The name shown on the screen and printed in the title is taken from the file specification at 5242H: up to Register B characters, in capitals, ending at the period of the extension, the colon of the drive or 0DH, at 59C8H-59D5H; a colon follows, and the place after it is kept at 6027H for the drive digit.

65E5H - Show a Text

65E5H copies the text at Register Pair HL to Register Pair DE up to the byte with bit 7 set, whose bit 7 it clears at the destination; it returns Register Pair HL at that last byte and Register Pair DE after the copy. 65F5H shows a text at 3FEEH.

65FFH - The Cursor Keys

The arrow keys move the cursor of the record: LEFT and RIGHT ARROW one byte, UP and DOWN ARROW one row of 16 bytes, SHIFT UP ARROW to byte 00H. A move that would leave the record is not made. The 128 byte mode scrolls its window when the cursor leaves it; the offset and, in the 128 byte mode, the value of the byte are shown again.

66DFH - H: Hex Modify

In the hex modify mode the first hex digit typed replaces the first digit of the byte at the cursor on the screen, and the byte of the edit buffer becomes the value of the two digits shown; the second digit replaces the second, the byte is stored again, and the cursor moves to the next byte (unless it is on the last). The ASCII column shows the new byte. Any other key at the first digit is taken as an arrow key or ignored; at the second digit it is ignored.

6737H - A: ASCII Modify

In the ASCII modify mode each key (but BREAK and the arrows, taken before) is stored in the byte at the cursor, shown in the ASCII column (as 88H when it is a control code or above 7FH) and in hex, and the cursor moves to the next byte. A key with bit 7 set is ignored.

6791H - The Command Line

The command line is kept at 5962H; 6016H points at the place of the next character. 67BCH stores a character there and at the cursor of the video, 6791H also moves the place on and puts a space after it, 679FH clears the line, puts the cursor at the command and sets the state to 00H, and 67C6H puts the cursor at the command (3FFFH in the 256 byte mode, 3FC8H in the 128 byte mode).

67DBH - Cursors Off; Hex Digits and Keys

67DBH takes the blinking cursors off the screen before the screen or the record changes. 67F2H and 67FBH turn two hex digits into a byte; 6818H and 6821H test for a digit and a hex digit. 682FH takes a key: BREAK clears the command and the boxes, and the letters are made capitals except for C, F and A. 685DH ends FED; 6870H clears the input line of the 128 byte mode; 6880H turns a byte into two hex digits.

68A5H - Numbers in Decimal and Hex

68A5H writes Register Pair DE in decimal at 68F9H without leading zeros by subtracting the powers of ten at 68EFH, and returns the count of the digits in Register B and Register Pair HL = 68F9H. 68FEH writes Register Pair DE as four hex digits at 68F9H and returns Index Register IX = 68F9H. 692EH takes the hex digits at Register Pair HL into Register Pair DE.

6953H - The Display of the 256 Byte Mode

The screen image at 5562H is cleared and the record drawn into it: the 16 rows of the record as characters (columns 0-15), a bar, the row labels 00-F0 with 3EH after them, and the 128 words in hex, eight to a row from column 21. The right edge holds the record number down column 61 in a box, an asterisk below it for the last record, the name of the file down column 63, the offset after 3EH on row 14 and C: on row 15. The 128 byte mode is built at 6A62H instead.

6A24H - The Record Number and the Last Record

6A24H writes the number of the record (6021H) in four hex digits: down a column from Register Pair HL in the 256 byte mode (559FH in the screen image, or 3C3DH on the screen during a search), across row 3 at 3CC5H in the 128 byte mode. 6A49H puts an asterisk under the number (56DFH), or at Register Pair DE after the title in the 128 byte mode, when the record is the last.

6A62H - The Display of the 128 Byte Mode

The 128 byte mode shows a window of eight rows of the record: its 128 characters across rows 0-1, the column labels 00-0F on row 3, the hex bytes of each row with its label on rows 5-12 between two lines of 8CH, the title of the record on row 14 with Relative Byte and the offset, and Command: on row 15. The window starts at the row of the cursor when the cursor is outside it, at 80H at most.