BASIC file formats - Revision history

Mizapf: /* Sample program */

2019-05-30T19:43:00Z

Sample program

← Older revision		Revision as of 19:43, 30 May 2019
Line 59:		Line 59:
	== Sample program ==		== Sample program ==

	Let's have a look at a real Extended BASIC program. This is an output of [[TIImageTool]] which shows the contents of a [[PROGRAM]] file.		Let's have a look at a real Extended BASIC program. This is an output of [https://www.mizapf.de/ti99/timt TIImageTool] which shows the contents of a [[PROGRAM]] file.

	000000: 00 3f 37 a7 37 98 37 d7 00 28 37 a9 00 1e 37 ac .?7.7.7..(7...7.		000000: 00 3f 37 a7 37 98 37 d7 00 28 37 a9 00 1e 37 ac .?7.7.7..(7...7.

HackMac: add this article to an other category

2016-04-10T08:36:45Z

add this article to an other category

← Older revision		Revision as of 08:36, 10 April 2016
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	40 END		40 END

	[[Category:Programming]]		[[Category:Programming]] [[Category:File Format]]

Stefan Haubenthal: Category

2015-06-10T16:54:31Z

Mizapf at 17:55, 29 March 2015

2015-03-29T17:55:03Z

← Older revision		Revision as of 17:55, 29 March 2015
Line 6:		Line 6:

	BASIC lines are ''tokenized''. For each command or special character or character sequence that has a meaning in BASIC there is a one-byte code, the ''token''. Example:		BASIC lines are ''tokenized''. For each command or special character or character sequence that has a meaning in BASIC there is a one-byte code, the ''token''. Example:


	{\| class="plainc"		{\| class="plainc"
Line 36:		Line 37:
	\| fe		\| fe
	\|}		\|}


	You can find a [[BASIC tokens \| complete table]] here.		You can find a [[BASIC tokens \| complete table]] here.
Line 46:		Line 48:

	Finally, the line is converted to the following byte sequence:		Finally, the line is converted to the following byte sequence:


	{\| class="plainc"		{\| class="plainc"
Line 52:		Line 55:
	\| line length \|\| PRINT \|\| "..." \|\| string length \|\| H \|\| E \|\| L \|\| L \|\| O \|\| end		\| line length \|\| PRINT \|\| "..." \|\| string length \|\| H \|\| E \|\| L \|\| L \|\| O \|\| end
	\|}		\|}


	== Sample program ==		== Sample program ==
Line 80:		Line 84:

	Everything is still the same. We can now analyse the contents of the file. The memory location refers to the locations where the portions of the program will reside when we load it into memory with OLD.		Everything is still the same. We can now analyse the contents of the file. The memory location refers to the locations where the portions of the program will reside when we load it into memory with OLD.


	{\| class="plainc"		{\| class="plainc"
Line 116:		Line 121:
	\| style="text-align:left" \| 0e 8c 52 4f 57 be c8 01 31 b1 c8 02 32 30 00		\| style="text-align:left" \| 0e 8c 52 4f 57 be c8 01 31 b1 c8 02 32 30 00
	\|}		\|}


	==== Header ====		==== Header ====
Line 153:		Line 159:

	Now it is time to find out what the program line consists of. We will now replace the tokens by their respective texts; actually, we do what happens in the computer when we execute the LIST command. Moreover, we assign the line numbers from the LNT.		Now it is time to find out what the program line consists of. We will now replace the tokens by their respective texts; actually, we do what happens in the computer when we execute the LIST command. Moreover, we assign the line numbers from the LNT.


	{\| class="plainc"		{\| class="plainc"
Line 259:		Line 266:
	\| 00		\| 00
	\|}		\|}


	Only one thing is left. There are sequences of ASCII characters (52 4f 57 = "ROW") that are neither declared as quoted nor unquoted strings nor commands. For some obscure reason, TI decided to indicate variable names simply by the characters alone. No marker, no length byte.		Only one thing is left. There are sequences of ASCII characters (52 4f 57 = "ROW") that are neither declared as quoted nor unquoted strings nor commands. For some obscure reason, TI decided to indicate variable names simply by the characters alone. No marker, no length byte.
Line 268:		Line 276:
	30 NEXT ROW		30 NEXT ROW
	40 END		40 END

	~~'''TODO: continue'''~~

Mizapf: /* Header */

2015-03-29T17:53:05Z

Header

← Older revision		Revision as of 17:53, 29 March 2015
Line 132:		Line 132:
	003f = 0000000000111111		003f = 0000000000111111

	If this word is negated, the BASIC program is protected and cannot be listed. This is only available in ~~Extemded~~ BASIC.		If this word is negated, the BASIC program is protected and cannot be listed. This is only available in Extended BASIC.

	==== Line number table ====		==== Line number table ====

Mizapf at 17:52, 29 March 2015

2015-03-29T17:52:37Z

@@ Line 1: / Line 1: @@
 BASIC programs written for TI BASIC and [[Extended BASIC]] are not stored as plain text in memory. This is different with assembler programs which are edited as text files and then assembled to a [[Tagged Object Code]] file.
@@ Line 51: / Line 53: @@
 |}
-=== Sample program ===
+== Sample program ==
 Let's have a look at a real Extended BASIC program. This is an output of [[TIImageTool]] which shows the contents of a [[PROGRAM]] file.
@@ Line 186: / Line 188: @@
 Next, we replace all tokens in the lines as we find them in the [[BASIC tokens | table]].
 {| class="plainc"
@@ Line 218: / Line 221: @@
 | 00
 |}
 '''TODO: continue'''

Mizapf at 17:43, 29 March 2015

2015-03-29T17:43:10Z

@@ Line 150: / Line 150: @@
 * The first byte is a length byte. The length byte does not count itself, but includes the 00 byte at the end.
-Now it is time to find out what the program line consists of. We will now replace the tokens by their respective texts; actually, we do what happens in the computer when we execute the LIST command.
+Now it is time to find out what the program line consists of. We will now replace the tokens by their respective texts; actually, we do what happens in the computer when we execute the LIST command. Moreover, we assign the line numbers from the LNT.
 '''TODO: continue'''

Mizapf at 17:31, 29 March 2015

2015-03-29T17:31:34Z

← Older revision		Revision as of 17:31, 29 March 2015
Line 77:		Line 77:
	0e 8c 52 4f 57 be c8 01 31 b1 c8 02 32 30 00		0e 8c 52 4f 57 be c8 01 31 b1 c8 02 32 30 00

	Everything is still the same. We can now analyse the contents of the file.		Everything is still the same. We can now analyse the contents of the file. The memory location refers to the locations where the portions of the program will reside when we load it into memory with OLD.

	{\| class="plainc"		{\| class="plainc"
	! Meaning		! Meaning
			! Memory location
	! Contents		! Contents
	\|-		\|-
	\| Header		\| Header
			\|
	\| style="text-align:left" \| 003f 37a7 3798 37d7		\| style="text-align:left" \| 003f 37a7 3798 37d7
	\|-		\|-
	\| rowspan="4" \| Line Number Table		\| rowspan="4" \| Line Number Table
			\| '''3798''' - 379b
	\| style="text-align:left" \|0028 37a9		\| style="text-align:left" \|0028 37a9
	\|-		\|-
			\| 379c - 379f
	\| style="text-align:left" \|001e 37ac		\| style="text-align:left" \|001e 37ac
	\|-		\|-
			\| 37a0 - 37a3
	\| style="text-align:left" \| 0014 37b2		\| style="text-align:left" \| 0014 37b2
	\|-		\|-
			\| 37a4 - '''37a7'''
	\| style="text-align:left" \| 000a 37ca		\| style="text-align:left" \| 000a 37ca
	\|-		\|-
	\| rowspan="4" \| Program lines		\| rowspan="4" \| Program lines
			\| 37a8 - 37aa
	\| style="text-align:left" \| 02 8b 00		\| style="text-align:left" \| 02 8b 00
	\|-		\|-
			\| 37ab - 37b0
	\| style="text-align:left" \| 05 96 52 4f 57 00		\| style="text-align:left" \| 05 96 52 4f 57 00
	\|-		\|-
			\| 37b1 - 37c8
	\| style="text-align:left" \| 17 a2 f0 b7 52 4f 57 b3 c8 01 31 b6 b5 c7 04 54 45 53 54 b4 52 4f 57 00		\| style="text-align:left" \| 17 a2 f0 b7 52 4f 57 b3 c8 01 31 b6 b5 c7 04 54 45 53 54 b4 52 4f 57 00
	\|-		\|-
			\| 37c9 - '''37d7'''
	\| style="text-align:left" \| 0e 8c 52 4f 57 be c8 01 31 b1 c8 02 32 30 00		\| style="text-align:left" \| 0e 8c 52 4f 57 be c8 01 31 b1 c8 02 32 30 00
	\|}		\|}

			==== Header ====

			The file starts with a header, containing four 16-bit words. When you carefully look at the table above, you can already deduce how those numbers are calculated.

			* The second word is the start of the line number table.
			* The third word is the end of the line number table.
			* The fourth word is the end of available memory. Programs are always loaded so that their last byte falls on the highest available address.

			The first word is calculated as the XOR of the addresses of the start and end of the line number table:

			37a7 = 0011011110100111
			XOR 3798 = 0011011110011000
			-----------------------
			003f = 0000000000111111

			If this word is negated, the BASIC program is protected and cannot be listed. This is only available in Extemded BASIC.

			==== Line number table ====

			The next block is the line number table (LNT). Again, when you look carefully you see that we have a list of entries, each of which contains two 16-bit words:

			* The first word is the line number.
			* The second word is the location of the BASIC line in memory.

			To be precise, the memory location is the second byte of a BASIC line. For example, the fourth entry (000a 37ca) tells us that the line in memory at address 37c9 is BASIC line 10.

			Another interesting point is that the LNT is sorted, with the highest line number appearing at the low end, and the lowest number at the high end. In our example, the line numbers are 000a (10), 0014 (20), 001e (30), and 0028 (40). Moreover, the BASIC lines seem to be sorted in the same way, with the contents of line 10 near the memory end, and later lines growing towards lower memory.

			==== BASIC line ====

			What remains are the tokenized lines. Again, here are two things we can quickly find out.

			* The last byte of each line is 00.
			* The first byte is a length byte. The length byte does not count itself, but includes the 00 byte at the end.

			Now it is time to find out what the program line consists of. We will now replace the tokens by their respective texts; actually, we do what happens in the computer when we execute the LIST command.




	'''TODO: continue'''		'''TODO: continue'''

Mizapf at 13:00, 29 March 2015

2015-03-29T13:00:34Z

@@ Line 43: / Line 43: @@
 There will not be a string like "PRINT" in memory, because the parser recognized this word as a command and replaced it with its token. Second, there is a string following the command, which is enclosed in quotes. The contents can be anything, so the parser must copy it into memory as is.
-Eventually, the line is converted to the following byte sequence:
+Finally, the line is converted to the following byte sequence:
 {| class="plainc"
@@ Line 51: / Line 51: @@
 |}
 '''TODO: continue'''

Mizapf at 01:00, 29 March 2015

2015-03-29T01:00:37Z

← Older revision		Revision as of 01:00, 29 March 2015
Line 36:		Line 36:

	You can find a [[BASIC tokens \| complete table]] here.		You can find a [[BASIC tokens \| complete table]] here.

			So let us take a simple BASIC line like

			PRINT "HELLO"

			There will not be a string like "PRINT" in memory, because the parser recognized this word as a command and replaced it with its token. Second, there is a string following the command, which is enclosed in quotes. The contents can be anything, so the parser must copy it into memory as is.

			Eventually, the line is converted to the following byte sequence:

			{\| class="plainc"
			\| 09 \|\| 9c \|\| c7 \|\| 05 \|\| 48 \|\| 45 \|\| 4c \|\| 4c \|\| 4f \|\| 00
			\|-
			\| line length \|\| PRINT \|\| "..." \|\| string length \|\| H \|\| E \|\| L \|\| L \|\| O \|\| end
			\|}


	'''TODO: continue'''		'''TODO: continue'''

← Older revision		Revision as of 16:54, 10 June 2015
Line 276:		Line 276:
	30 NEXT ROW		30 NEXT ROW
	40 END		40 END

			[[Category:Programming]]