7800 HSC Technical Reference - Revision history

MSaarna at 22:54, 2 October 2026

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MSaarna at 22:52, 2 October 2026

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MSaarna at 22:50, 2 October 2026

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MSaarna at 22:42, 2 October 2026

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MSaarna at 18:27, 2 October 2026

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MSaarna at 18:03, 2 October 2026

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MSaarna at 18:03, 2 October 2026

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MSaarna at 17:59, 2 October 2026

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MSaarna at 16:32, 1 October 2026

2026-10-01T16:32:54Z

MSaarna at 16:29, 1 October 2026

2026-10-01T16:29:07Z

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 The '''Atari 7800 High Score Cartridge (HSC)''' is an expansion peripheral that provides battery-backed RAM (NVRAM) and a standard high score service for Atari 7800 games. It uses a pass-through design: the HSC plugs into the 7800 cartridge slot, and the game cartridge plugs into the top of the HSC.
-This page covers both the game-facing interface and the internals of the original Atari ROM (<code>highscre.bin</code>, 4096 bytes, MD5 <code>c8a73288ab97226c52602204ab894286</code>). Internal addresses below refer to that ROM. The 2026 community disassembly ([[7800 HSC CART]]) reassembles byte-identical with DASM, and its labels are used here.
+This page covers both the game-facing interface and the internals of the ROM (<code>highscre.bin</code>, 4096 bytes, MD5 <code>c8a73288ab97226c52602204ab894286</code>). Internal addresses below refer to that ROM. The 2026 community disassembly ([[7800 HSC CART]]) reassembles byte-identical with DASM, and its labels are used here.
 == System Architecture & Memory Map ==
@@ Line 254: / Line 254: @@
 Games pass 8-digit packed BCD. NVRAM holds a '''24-bit binary''' value, little-endian.
-# '''Clamp''' (<code>$3A83</code>): the score is compared byte by byte with <code>$16 $77 $72 $15</code> (16,777,215). If it's larger, the maximum is '''written back into the game's score''' and used instead. The comparison is signed, see [[#Bugs and quirks in the original ROM|bugs]].
+# '''Clamp''' (<code>$3A83</code>): the score is compared byte by byte with <code>$16 $77 $72 $15</code> (16,777,215). If it's larger, the maximum is '''written back into the game's score''' and used instead. The comparison is signed, see [[#Bugs and quirks in the ROM|bugs]].
-# '''Convert''' (<code>$3AA8</code>): for each nibble, the value is multiplied by 10 (<code>$3A5E</code>, a full 24-bit ×10) and the nibble is added. The result goes in <code>$AD</code> (LSB), <code>$AE</code>, <code>$AF</code> (MSB). The nibble add has a carry bug, see [[#Bugs and quirks in the original ROM|bugs]].
+# '''Convert''' (<code>$3AA8</code>): for each nibble, the value is multiplied by 10 (<code>$3A5E</code>, a full 24-bit ×10) and the nibble is added. The result goes in <code>$AD</code> (LSB), <code>$AE</code>, <code>$AF</code> (MSB). The nibble add has a carry bug, see [[#Bugs and quirks in the ROM|bugs]].
 # '''Display''' (<code>$37BC</code>): the value is turned into decimal by repeated subtraction of the powers of ten at <code>$3EC7</code>, giving a 9-character field:
 #* ID1 bit 7 clear: a leading space, then 8 digits with leading zeros blanked. The last digit always shows.
@@ Line 385: / Line 385: @@
 The community "PAL hack" (<code>PALHACK</code> in the disassembly) only lengthens the gap zones.
-== Bugs and Quirks in the Original ROM ==
+== Bugs and Quirks in the HSC ROM ==
 {| class="wikitable"

@@ Line 388: / Line 388: @@
 {| class="wikitable"
-! # !! Where !! Behavior !! Effect !! Clean-room ROM
+! # !! Where !! Behavior !! Effect
 |-
-| 1 || <code>$3ABB</code>, <code>$3ACC</code> || '''Carry lost in BCD→binary conversion.''' After each nibble is added to the low byte, the carry goes into the middle byte with <code>ADC #$00</code> but never on into the high byte (<code>$AF</code>). || Whenever the running value crosses a multiple of 65,536 during a nibble add, 65,536 is lost. 65,536 → 0, 131,072 → 65,536, '''655,360 → 0''', which can then never rank. 14 multiples of 10 below 2,000,000 are affected. || fixed
+| 1 || <code>$3ABB</code>, <code>$3ACC</code> || '''Carry lost in BCD→binary conversion.''' After each nibble is added to the low byte, the carry goes into the middle byte with <code>ADC #$00</code> but never on into the high byte (<code>$AF</code>). || Whenever the running value crosses a multiple of 65,536 during a nibble add, 65,536 is lost. 65,536 → 0, 131,072 → 65,536, '''655,360 → 0''', which can then never rank. 14 multiples of 10 below 2,000,000 are affected.
 |-
-| 2 || <code>$3A8B–$3A91</code> || '''Signed clamp compare.''' <code>CMP</code> then <code>BMI/BPL</code> tests the sign of (limit − score) instead of the carry. || First byte <code>$97–$99</code> (scores ≥ 97,000,000) isn't clamped, and neither is <code>$16 $77 $72</code> followed by <code>$96–$99</code>. Those values wrap modulo 2^24. || fixed
+| 2 || <code>$3A8B–$3A91</code> || '''Signed clamp compare.''' <code>CMP</code> then <code>BMI/BPL</code> tests the sign of (limit − score) instead of the carry. || First byte <code>$97–$99</code> (scores ≥ 97,000,000) isn't clamped, and neither is <code>$16 $77 $72</code> followed by <code>$96–$99</code>. Those values wrap modulo 2^24.
 |-
-| 3 || <code>$3A93</code> || The clamp writes the maximum back into the game's score bytes, on every vector, including HSCATRCT and the copy calls. || A game showing its score after an HSC call shows 16,777,215. || kept (only for real overflows)
+| 3 || <code>$3A93</code> || The clamp writes the maximum back into the game's score bytes, on every vector, including HSCATRCT and the copy calls. || A game showing its score after an HSC call shows 16,777,215.
 |-
-| 4 || <code>$31D7</code> || HSCENTER2 initials aren't masked to 5 bits. || A value above <code>$1F</code> in initial 1 or 3 corrupts initial 2's packed bits. || fixed (masked)
+| 4 || <code>$31D7</code> || HSCENTER2 initials aren't masked to 5 bits. || A value above <code>$1F</code> in initial 1 or 3 corrupts initial 2's packed bits.
 |-
-| 5 || <code>$36AB</code> || The 26-byte difficulty-name copy runs even when its pointer's high byte is 0. || Reads zero page and TIA/MARIA addresses. Harmless on stock hardware. || fixed
+| 5 || <code>$36AB</code> || The 26-byte difficulty-name copy runs even when its pointer's high byte is 0. || Reads zero page and TIA/MARIA addresses. Harmless on stock hardware.
 |-
-| 6 || <code>$3C2D</code> || The hold timer is decremented and tested with <code>BMI</code>. || Hold values <code>$81–$FF</code> behave like 0; <code>$80</code> holds for 128 s. || kept
+| 6 || <code>$3C2D</code> || The hold timer is decremented and tested with <code>BMI</code>. || Hold values <code>$81–$FF</code> behave like 0; <code>$80</code> holds for 128 s.
 |-
-| 7 || <code>$3318</code> || BACKSPACE stores the ← glyph in the position it leaves. || The ← stays on screen, and moving right again starts on ←. || may be improved
+| 7 || <code>$3318</code> || BACKSPACE stores the ← glyph in the position it leaves. || The ← stays on screen, and moving right again starts on ←.
 |-
-| 8 || <code>$392C</code> || The screen-saver wake-up reads the raw ports. || Driver-based controllers can't wake the screen. || kept
+| 8 || <code>$392C</code> || The screen-saver wake-up reads the raw ports. || Driver-based controllers can't wake the screen.
 |-
-| 9 || <code>$392C</code> || The screen saver ends with SWACNT = SWBCNT = 0. || A game's two-button-mode setup is lost after a long idle period. || kept
+| 9 || <code>$392C</code> || The screen saver ends with SWACNT = SWBCNT = 0. || A game's two-button-mode setup is lost after a long idle period.
 |-
-| 10 || <code>$3022</code> || HSCSTAT reports <code>$FF</code> when no table exists, even for scores HSCENTER would accept. || Games must call HSCENTER for any nonzero score to get their first table. || kept
+| 10 || <code>$3022</code> || HSCSTAT reports <code>$FF</code> when no table exists, even for scores HSCENTER would accept. || Games must call HSCENTER for any nonzero score to get their first table.
 |-
-| 11 || <code>$35A1</code> || The touch loop also increments the slot it just zeroed. || The most recently used age is 1, not 0. || kept (save format)
+| 11 || <code>$35A1</code> || The touch loop also increments the slot it just zeroed. || The most recently used age is 1, not 0.
 |-
-| 12 || <code>$3C95</code> || First-use formatting during HSCSTAT runs the personalization screen and returns with DMA off. || Games that call HSCSTAT at boot show a naming screen on a fresh cart. || kept
+| 12 || <code>$3C95</code> || First-use formatting during HSCSTAT runs the personalization screen and returns with DMA off. || Games that call HSCSTAT at boot show a naming screen on a fresh cart.
 |-
-| 13 || <code>$3242</code> || Fire isn't required to be released before entry starts. || A button still held from gameplay accepts the first initial on release. || kept
+| 13 || <code>$3242</code> || Fire isn't required to be released before entry starts. || A button still held from gameplay accepts the first initial on release.
 |-
-| 14 || <code>$36DE</code>, <code>$3715</code> || <code>$B9</code> is both the logo-DLI flag and the screen-saver timer. || Harmless; worth knowing when reading the code. || n/a
+| 14 || <code>$36DE</code>, <code>$3715</code> || <code>$B9</code> is both the logo-DLI flag and the screen-saver timer. || Harmless; worth knowing when reading the code.
 |-
-| 15 || <code>$3F6E</code> || A stray letter 'A' between two strings is never referenced. || None. || n/a
+| 15 || <code>$3F6E</code> || A stray letter 'A' between two strings is never referenced. || None.
 |}

← Older revision		Revision as of 22:50, 2 October 2026
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	== Bugs and Quirks in the Original ROM ==		== Bugs and Quirks in the Original ROM ==
−
−	~~These were found while preparing a clean-room replacement for the Voxy emulator. The replacement fixes the ones marked '''fixed''' and keeps the others.~~

	{\| class="wikitable"		{\| class="wikitable"

@@ Line 281: / Line 281: @@
 | <code>$10B3–$10F7</code> || 69 || <code>CartRAMGameDifficultyTable</code> || Difficulty (<code>& $FC</code>) per slot. <code>$7F</code> = free
 |-
-| <code>$10F8–$113C</code> || 69 || <code>CartRAMGameIndexTable</code> || LRU age per slot. <code>$7F</code> = free
+| <code>$10F8–$113C</code> || 69 || <code>CartRAMGameAgeTable</code> || LRU age per slot. <code>$7F</code> = free
 |-
 | <code>$113D–$17F9</code> || 1725 || — || 69 tables × 25 bytes; slot s at <code>$113D + 25·s</code>
 |-
-| <code>$17FA–$17FE</code> || 5 || <code>CartRAMTempScore</code> || Copy of the displaced 5th-place entry during HSCENTER, used to undo a cancel
+| <code>$17FA–$17FE</code> || 5 || <code>CartRAMSavedEntry</code> || Copy of the displaced 5th-place entry during HSCENTER, used to undo a cancel
 |-
 | <code>$17FF</code> || 1 || — || Unused

@@ Line 3: / Line 3: @@
 The '''Atari 7800 High Score Cartridge (HSC)''' is an expansion peripheral that provides battery-backed RAM (NVRAM) and a standard high score service for Atari 7800 games. It uses a pass-through design: the HSC plugs into the 7800 cartridge slot, and the game cartridge plugs into the top of the HSC.
-This page covers both the game-facing interface and the internals of the original Atari ROM (<code>highscre.bin</code>, 4096 bytes, MD5 <code>c8a73288ab97226c52602204ab894286</code>). Internal addresses below refer to that ROM. The 2026 community disassembly (<code>high_score_cart.asm</code>, by Mark Ball and Mike Saarna, with later annotation) reassembles byte-identical with DASM, and its labels are used here.
+This page covers both the game-facing interface and the internals of the original Atari ROM (<code>highscre.bin</code>, 4096 bytes, MD5 <code>c8a73288ab97226c52602204ab894286</code>). Internal addresses below refer to that ROM. The 2026 community disassembly ([[7800 HSC CART]]) reassembles byte-identical with DASM, and its labels are used here.
 == System Architecture & Memory Map ==

@@ Line 210: / Line 210: @@
 === Character Set & Font ===
-The HSC uses its own character codes, often called '''Watkins encoding'''. Letters are <code>'X' - 'A'</code>. The table below was checked by rendering the font from the ROM; earlier tables had several codes wrong.
+The HSC uses its own character codes, often called '''Watkins encoding'''. Letters are <code>'X' - 'A'</code>.
 {| class="wikitable" style="text-align: center;"
@@ Line 247: / Line 247: @@
 * Packing: <code>EncodeAndSaveInitialsToTable</code>, <code>$31D7</code>. Unpacking: <code>$3AD6</code>.
-* Empty entries hold <code>___</code> (three underscores, <code>$1A $1A $1A</code>), packed as <code>$DA $9A</code>. These were previously described as "...", which is wrong: <code>$1A</code> is the underscore.
+* Empty entries hold <code>___</code> (three underscores, <code>$1A $1A $1A</code>), packed as <code>$DA $9A</code>.
 * Other examples: <code>ABC</code> = <code>$00 $42</code>, <code>XYZ</code> = <code>$D7 $19</code>.
@@ Line 335: / Line 335: @@
 '''Stepping through characters.''' The stick is sampled every 10 frames:
 * '''Up/Right''' = next: A…Z, _, ., -, space, ', █, ←, then A. At position 0 the ← is skipped.
-* '''Down/Left''' = previous, the same cycle backwards. The disassembly comments have these two directions the wrong way round.
+* '''Down/Left''' = previous, the same cycle backwards.
 * Pressing Next on <code>_</code> as the first move at a position jumps straight to 'A'.
 * Position 3 offers only █ (END) and ← (BACKSPACE).

@@ Line 326: / Line 326: @@
 * '''LRU Eviction:''' If all 69 slots are occupied and a new game or difficulty is registered, the slot with the highest aging index in <code>CartRAMGameIndexTable</code> is purged and replaced.
 * '''Table Address Formula:'''
-:<math>\text{TableAddress} = \$113D + (\text{SlotIndex} \times 25)</math>
+<pre>TableAddress = $113D + (SlotIndex * 25)</pre>
 * Each 25-byte block stores 5 entries of 5 bytes each, ordered from 1st place (offset <code>+$00</code>) to 5th place (offset <code>+$14</code>).

@@ Line 1: / Line 1: @@
-= Atari 7800 High Score Cartridge (HSC) Technical Reference & Integration Guide =
+= Atari 7800 High Score Cartridge (HSC) Technical Reference =
 The '''Atari 7800 High Score Cartridge (HSC)''' is an expansion peripheral that provides non-volatile battery-backed RAM (NVRAM) and a standardized high-score interface for Atari 7800 games. It connects via a pass-through architecture: the HSC plugs into the 7800 cartridge slot, and the game cartridge plugs into the top of the HSC.
@@ Line 99: / Line 99: @@
 |}
 === Calling Conventions ===