Fastload is a dual-speed bootstrap generator for the ZX81/TS1000 that embeds a short machine-code routine in a REM statement at line 1 and executes it via RAND USR 16514. The machine code (visible as raw bytes in the REM) performs a fast-load bootstrap operation, allowing programs to be saved and loaded at accelerated speeds. To use it, the operator must POKE 16389,76 to minimize the display buffer, delete the directions at line 200, rename line 100’s SAVE target, then execute the program from line 1 while the tape is running. After saving, the machine-code monitor is used to append the desired program data after the loader on tape.
Program Analysis
Program Structure
The program is minimal in terms of BASIC lines but carries its real payload inside a REM statement:
Line 1— REM containing 21 raw machine-code bytes, positioned at address 16514 (the first byte after the REM token and length bytes in a ZX81 program).Line 100—SAVE "ANY DESIRED FILENAME", which the user is instructed to rename before use.Line 110—RAND USR 16514, which transfers control to the machine code in the REM.Line 200— A lengthy REM containing inverse-video instructions for the end user, intended to be deleted before the final save.
Machine Code in the REM
The bytes stored in line 1’s REM are:
| Offset | Hex | Mnemonic (Z80) |
|---|---|---|
| 0 | 2A 10 40 | LD HL,(4010h) — load HL with the value at address 16400 (VARS) |
| 3 | 01 06 00 | LD BC,0006h |
| 6 | 09 | ADD HL,BC |
| 7 | 11 94 7E | LD DE,7E94h |
| 10 | 01 6C 01 | LD BC,016Ch |
| 13 | ED A0 | LDI — block copy one byte (HL)→(DE), decrement BC |
| 15 | EA 8F 40 | JP PE,408Fh — jump if parity/overflow (BC≠0) to address 16527; effectively loops… but this is a single LDI, so this is more likely a computed jump for bootstrap setup |
| 18 | C3 CB 7F | JP 7FCBh — jump to address 32715, the fast-load entry point |
The routine reads the VARS pointer from system variable VARS (16400), adds 6, then uses that as a source address for a block copy into high RAM near 7E94h, and finally jumps to 7FCBh. This relocates data out of the BASIC variable area into a fixed high-memory location before handing off to the fast-loader code stored there.
Setup Procedure
The directions in line 200 describe a precise six-step workflow:
- POKE 16389,76 to reduce the display file to its minimum, maximizing available RAM below the machine code.
- Enter
NEWand reload the program to apply the minimized display buffer. - Delete line 200 (the directions REM) to reduce program size.
- Edit line 100 to set the desired SAVE filename for the final auto-start loader.
- Issue
CLS, typeGOTO 1but hold ENTER until the tape is running. - After the bootstrap saves itself, use a machine-code monitor to append the target program to the tape image after the loader.
Key BASIC Idioms
RAND USR 16514 is the standard ZX81/TS1000 idiom for calling machine code embedded in a REM at line 1. Because line 1’s REM token occupies bytes at address 16509 and the data begins after the REM opcode, line-length word, and newline, the actual code starts at 16514. Using RAND rather than LET discards the USR return value silently, avoiding a variable being created.
Notable Techniques
- The machine code is entirely self-contained in a single REM line, requiring no separate POKE sequence to install it.
- The final
JP 7FCBhassumes a secondary fast-loader binary already resides at7FCBhin RAM — this would be the “dual-speed” component loaded or resident separately, consistent with the instructions to use a machine-code monitor to append it. - The POKE 16389,76 step sets the system variable
D_FILElow byte to collapse the display file, a well-known ZX81 technique to reclaim RAM for machine code in the upper address space. - All user-facing instructions are encoded in inverse video inside the REM at line 200, making them visually distinct on screen while remaining harmlessly ignored by the interpreter.
Bugs and Anomalies
The single LDI at offset 13 copies only one byte before the JP PE instruction. Since LDI decrements BC and sets the P/V flag if BC≠0 after the operation, with BC=016Ch (364 decimal) the jump back would loop — but the destination 408Fh (16527) is two bytes past the end of the REM data, pointing into subsequent program lines. This suggests the block-copy loop is intentional and 408Fh re-enters the LDI instruction in a self-modifying or positionally-dependent way, or that the listing as printed has been slightly truncated. The overall design is consistent with a working fast-loader tool despite this apparent ambiguity.
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Source Code
1 REM
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Fastload
Fastload is a dual-speed bootstrap generator for the ZX81/TS1000 that embeds a short machine-code routine in a REM statement at line 1 and executes it via RAND USR 16514. The machine code (visible as raw bytes in the REM) performs a fast-load bootstrap operation, allowing programs to be saved and loaded at accelerated speeds. To use it, the operator must POKE 16389,76 to minimize the display buffer, delete the directions at line 200, rename line 100’s SAVE target, then execute the program from line 1 while the tape is running. After saving, the machine-code monitor is used to append the desired program data after the loader on tape.
Program Analysis
Program Structure
The program is minimal in terms of BASIC lines but carries its real payload inside a REM statement:
Line 1 — REM containing 21 raw machine-code bytes, positioned at address 16514 (the first byte after the REM token and length bytes in a ZX81 program).Line 100 — SAVE "ANY DESIRED FILENAME", which the user is instructed to rename before use.Line 110 — RAND USR 16514, which transfers control to the machine code in the REM.Line 200 — A lengthy REM containing inverse-video instructions for the end user, intended to be deleted before the final save.
Machine Code in the REM
The bytes stored in line 1’s REM are:
Offset Hex Mnemonic (Z80) 0 2A 10 40LD HL,(4010h) — load HL with the value at address 16400 (VARS) 3 01 06 00LD BC,0006h 6 09ADD HL,BC 7 11 94 7ELD DE,7E94h 10 01 6C 01LD BC,016Ch 13 ED A0LDI — block copy one byte (HL)→(DE), decrement BC 15 EA 8F 40JP PE,408Fh — jump if parity/overflow (BC≠0) to address 16527; effectively loops… but this is a single LDI, so this is more likely a computed jump for bootstrap setup 18 C3 CB 7FJP 7FCBh — jump to address 32715, the fast-load entry point
The routine reads the VARS pointer from system variable VARS (16400), adds 6, then uses that as a source address for a block copy into high RAM near 7E94h, and finally jumps to 7FCBh. This relocates data out of the BASIC variable area into a fixed high-memory location before handing off to the fast-loader code stored there.
Setup Procedure
The directions in line 200 describe a precise six-step workflow:
- POKE 16389,76 to reduce the display file to its minimum, maximizing available RAM below the machine code.
- Enter
NEW and reload the program to apply the minimized display buffer.
- Delete line 200 (the directions REM) to reduce program size.
- Edit line 100 to set the desired SAVE filename for the final auto-start loader.
- Issue
CLS, type GOTO 1 but hold ENTER until the tape is running.
- After the bootstrap saves itself, use a machine-code monitor to append the target program to the tape image after the loader.
Key BASIC Idioms
RAND USR 16514 is the standard ZX81/TS1000 idiom for calling machine code embedded in a REM at line 1. Because line 1’s REM token occupies bytes at address 16509 and the data begins after the REM opcode, line-length word, and newline, the actual code starts at 16514. Using RAND rather than LET discards the USR return value silently, avoiding a variable being created.
Notable Techniques
- The machine code is entirely self-contained in a single REM line, requiring no separate POKE sequence to install it.
- The final
JP 7FCBh assumes a secondary fast-loader binary already resides at 7FCBh in RAM — this would be the “dual-speed” component loaded or resident separately, consistent with the instructions to use a machine-code monitor to append it.
- The POKE 16389,76 step sets the system variable
D_FILE low byte to collapse the display file, a well-known ZX81 technique to reclaim RAM for machine code in the upper address space.
- All user-facing instructions are encoded in inverse video inside the REM at line 200, making them visually distinct on screen while remaining harmlessly ignored by the interpreter.
Bugs and Anomalies
The single LDI at offset 13 copies only one byte before the JP PE instruction. Since LDI decrements BC and sets the P/V flag if BC≠0 after the operation, with BC=016Ch (364 decimal) the jump back would loop — but the destination 408Fh (16527) is two bytes past the end of the REM data, pointing into subsequent program lines. This suggests the block-copy loop is intentional and 408Fh re-enters the LDI instruction in a self-modifying or positionally-dependent way, or that the listing as printed has been slightly truncated. The overall design is consistent with a working fast-loader tool despite this apparent ambiguity.
Content
Image Gallery
Source Code
1 REM \2A\10\40\01\06\00\09\11\94\7E\01\6C\01\ED\A0\EA\8F\40\C3\CB\7F
100 SAVE "ANY DESIRED FILENAME"
110 RAND USR 16514
200 REM %(%C%)% %1%9%8%2 INTERNATIONAL PUBLISHING AND SOFTWARE INC. %"%D%U%A%L%-%S%P%E%E%D% %B%O%O%T%S%T%R%A%P% %G%E%N%E%R%A%T%O%R%"\''\''\''\''\''\''\':%D%I%R%E%C%T%I%O%N%S% %F%O%R% %U%S%E\:'\''\''\''\''\''\''%(%1%) \ :%P%O%K%E% %1%6%3%8%9%,%7%6\: ,\ :%N%E%W\: , AND \ :%L%O%A%D\: THIS PROGRAM TO GET MIN. DISPLAY BUFFER. %(%2%) DELETE LINE200. %(%3%) CHANGE LINE 100 SO THAT THE FINAL AUTO-START LOADERWILL\ :%L%O%A%D\: WITH THE DESIRED NAME.%(%4%) DO A\ :%C%L%S\: , TYPE\ :%G%O%T%O% %1\: , BUTDO NOT PRESS\ :%E%N%T%E%R\: YET. %(%5%) START TAPE AND PRESS\ :%E%N%T%E%R\: .THE PROGRAM WILL SAVE AN AUTO- START COPY OF ITSELF AND THEN HANG UP WITH "READ SILENCE" TV PATTERN AS IT TRIES TO LOAD SOMEPROGRAM. %(%6%) USING THE MACHINE- CODE MONITOR, SAVE THE DESIRED PROGRAM AFTER THE END OF THE LOADER.
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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Fastload
Fastload is a dual-speed bootstrap generator for the ZX81/TS1000 that embeds a short machine-code routine in a REM statement at line 1 and executes it via RAND USR 16514. The machine code (visible as raw bytes in the REM) performs a fast-load bootstrap operation, allowing programs to be saved and loaded at accelerated speeds. To use it, the operator must POKE 16389,76 to minimize the display buffer, delete the directions at line 200, rename line 100’s SAVE target, then execute the program from line 1 while the tape is running. After saving, the machine-code monitor is used to append the desired program data after the loader on tape.
Program Analysis
Program Structure
The program is minimal in terms of BASIC lines but carries its real payload inside a REM statement:
Line 1 — REM containing 21 raw machine-code bytes, positioned at address 16514 (the first byte after the REM token and length bytes in a ZX81 program).Line 100 — SAVE "ANY DESIRED FILENAME", which the user is instructed to rename before use.Line 110 — RAND USR 16514, which transfers control to the machine code in the REM.Line 200 — A lengthy REM containing inverse-video instructions for the end user, intended to be deleted before the final save.
Machine Code in the REM
The bytes stored in line 1’s REM are:
Offset Hex Mnemonic (Z80) 0 2A 10 40LD HL,(4010h) — load HL with the value at address 16400 (VARS) 3 01 06 00LD BC,0006h 6 09ADD HL,BC 7 11 94 7ELD DE,7E94h 10 01 6C 01LD BC,016Ch 13 ED A0LDI — block copy one byte (HL)→(DE), decrement BC 15 EA 8F 40JP PE,408Fh — jump if parity/overflow (BC≠0) to address 16527; effectively loops… but this is a single LDI, so this is more likely a computed jump for bootstrap setup 18 C3 CB 7FJP 7FCBh — jump to address 32715, the fast-load entry point
The routine reads the VARS pointer from system variable VARS (16400), adds 6, then uses that as a source address for a block copy into high RAM near 7E94h, and finally jumps to 7FCBh. This relocates data out of the BASIC variable area into a fixed high-memory location before handing off to the fast-loader code stored there.
Setup Procedure
The directions in line 200 describe a precise six-step workflow:
- POKE 16389,76 to reduce the display file to its minimum, maximizing available RAM below the machine code.
- Enter
NEW and reload the program to apply the minimized display buffer.
- Delete line 200 (the directions REM) to reduce program size.
- Edit line 100 to set the desired SAVE filename for the final auto-start loader.
- Issue
CLS, type GOTO 1 but hold ENTER until the tape is running.
- After the bootstrap saves itself, use a machine-code monitor to append the target program to the tape image after the loader.
Key BASIC Idioms
RAND USR 16514 is the standard ZX81/TS1000 idiom for calling machine code embedded in a REM at line 1. Because line 1’s REM token occupies bytes at address 16509 and the data begins after the REM opcode, line-length word, and newline, the actual code starts at 16514. Using RAND rather than LET discards the USR return value silently, avoiding a variable being created.
Notable Techniques
- The machine code is entirely self-contained in a single REM line, requiring no separate POKE sequence to install it.
- The final
JP 7FCBh assumes a secondary fast-loader binary already resides at 7FCBh in RAM — this would be the “dual-speed” component loaded or resident separately, consistent with the instructions to use a machine-code monitor to append it.
- The POKE 16389,76 step sets the system variable
D_FILE low byte to collapse the display file, a well-known ZX81 technique to reclaim RAM for machine code in the upper address space.
- All user-facing instructions are encoded in inverse video inside the REM at line 200, making them visually distinct on screen while remaining harmlessly ignored by the interpreter.
Bugs and Anomalies
The single LDI at offset 13 copies only one byte before the JP PE instruction. Since LDI decrements BC and sets the P/V flag if BC≠0 after the operation, with BC=016Ch (364 decimal) the jump back would loop — but the destination 408Fh (16527) is two bytes past the end of the REM data, pointing into subsequent program lines. This suggests the block-copy loop is intentional and 408Fh re-enters the LDI instruction in a self-modifying or positionally-dependent way, or that the listing as printed has been slightly truncated. The overall design is consistent with a working fast-loader tool despite this apparent ambiguity.
Content
Image Gallery
Source Code
1 REM \2A\10\40\01\06\00\09\11\94\7E\01\6C\01\ED\A0\EA\8F\40\C3\CB\7F
100 SAVE "ANY DESIRED FILENAME"
110 RAND USR 16514
200 REM %(%C%)% %1%9%8%2 INTERNATIONAL PUBLISHING AND SOFTWARE INC. %"%D%U%A%L%-%S%P%E%E%D% %B%O%O%T%S%T%R%A%P% %G%E%N%E%R%A%T%O%R%"\''\''\''\''\''\''\':%D%I%R%E%C%T%I%O%N%S% %F%O%R% %U%S%E\:'\''\''\''\''\''\''%(%1%) \ :%P%O%K%E% %1%6%3%8%9%,%7%6\: ,\ :%N%E%W\: , AND \ :%L%O%A%D\: THIS PROGRAM TO GET MIN. DISPLAY BUFFER. %(%2%) DELETE LINE200. %(%3%) CHANGE LINE 100 SO THAT THE FINAL AUTO-START LOADERWILL\ :%L%O%A%D\: WITH THE DESIRED NAME.%(%4%) DO A\ :%C%L%S\: , TYPE\ :%G%O%T%O% %1\: , BUTDO NOT PRESS\ :%E%N%T%E%R\: YET. %(%5%) START TAPE AND PRESS\ :%E%N%T%E%R\: .THE PROGRAM WILL SAVE AN AUTO- START COPY OF ITSELF AND THEN HANG UP WITH "READ SILENCE" TV PATTERN AS IT TRIES TO LOAD SOMEPROGRAM. %(%6%) USING THE MACHINE- CODE MONITOR, SAVE THE DESIRED PROGRAM AFTER THE END OF THE LOADER.
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.
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No people associated with this content.
E itemtype='https://schema.org/Blog' itemscope='itemscope' class="wp-singular computer_media-template-default single single-computer_media postid-51880 wp-custom-logo wp-embed-responsive wp-theme-astra wp-child-theme-astra-child ast-desktop ast-separate-container ast-left-sidebar astra-4.12.7 group-blog ast-blog-single-style-1 ast-custom-post-type ast-single-post ast-inherit-site-logo-transparent ast-hfb-header ast-full-width-primary-header ast-box-layout ast-normal-title-enabled astra-addon-4.12.5"C itemtype='https://schema.org/Blog' itemscope='itemscope' class="wp-singular computer_media-template-default single single-computer_media postid-51880 wp-custom-logo wp-embed-responsive wp-theme-astra wp-child-theme-astra-child ast-desktop ast-separate-container ast-left-sidebar astra-4.12.7 group-blog ast-blog-single-style-1 ast-custom-post-type ast-single-post ast-inherit-site-logo-transparent ast-hfb-header ast-full-width-primary-header ast-box-layout ast-normal-title-enabled astra-addon-4.12.5"\ED\A0\EAF\C3\CBF
100 SAVE "ANY DESIRED FILENAME"
110 RAND USR 16514
200 REM %(%C%)% %1%9%8%2 INTERNATIONAL PUBLISHING AND SOFTWARE INC. %"%D%U%A%L%-%S%P%E%E%D% %B%O%O%T%S%T%R%A%P% %G%E%N%E%R%A%T%O%R%"\''\''\''\''\''\''\':%D%I%R%E%C%T%I%O%N%S% %F%O%R% %U%S%E\:'\''\''\''\''\''\''%(%1%) \ :%P%O%K%E% %1%6%3%8%9%,%7%6\: ,\ :%N%E%W\: , AND \ :%L%O%A%D\: THIS PROGRAM TO GET MIN. DISPLAY BUFFER. %(%2%) DELETE LINE200. %(%3%) CHANGE LINE 100 SO THAT THE FINAL AUTO-START LOADERWILL\ :%L%O%A%D\: WITH THE DESIRED NAME.%(%4%) DO A\ :%C%L%S\: , TYPE\ :%G%O%T%O% %1\: , BUTDO NOT PRESS\ :%E%N%T%E%R\: YET. %(%5%) START TAPE AND PRESS\ :%E%N%T%E%R\: .THE PROGRAM WILL SAVE AN AUTO- START COPY OF ITSELF AND THEN HANG UP WITH "READ SILENCE" TV PATTERN AS IT TRIES TO LOAD SOMEPROGRAM. %(%6%) USING THE MACHINE- CODE MONITOR, SAVE THE DESIRED PROGRAM AFTER THE END OF THE LOADER.
Note: Type-in program listings on this website use ZMAKEBAS notation for graphics characters.