added som IMC-2001 subsections for chargen40 and firmware

3 files changed, 237 insertions, 0 deletions

diff --git a/content/hardware/imc-2001-chargen40.md b/content/hardware/imc-2001-chargen40.md
new file mode 100644
index 0000000..5c567a6
--- /dev/null
+++ b/content/hardware/imc-2001-chargen40.md
@@ -0,0 +1,88 @@
++++
+title = "IMC-2001 40 character mode"
++++
+
+*A4-A6* on the schematics is the character ROM in a chip labelled
+UMC UM2316-J127 8432, it is Intel 2716 EPROM compatible chip it seems.
+
+It can be read with the TL866 and returns the following 2K dump:
+
+[chargen.rom](/hardware/imc-2001/chargen.rom): Chargen 40-column ROM
+
+The official ROM
+[3410036.BIN](http://www.applelogic.org/APPLEASICs.html) on
+http://www.applelogic.org/APPLEASICs.html doesn't match
+at all. The arangement of the characters is different and there are
+lowercase characters in the clone ROM.
+
+I wrote a small program to show the contents of chargen.rom:
+
+```
+#!/usr/bin/tcc -run -Werror -DSDL_DISABLE_IMMINTRIN_H -I/usr/include/SDL2 -lSDL2
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <SDL.h>
+
+int main( int argc, char *argv[] )
+{
+	FILE *f = fopen( "./chargen.rom", "r" );
+	char *buf = malloc( 2 * 1024 );
+	fread( buf, 2 * 1024, 1, f );
+
+	SDL_Renderer *renderer;
+	SDL_Window *window;
+
+	SDL_Init( SDL_INIT_VIDEO );
+	SDL_CreateWindowAndRenderer( 300, 200, 0, &window, &renderer );
+	SDL_SetRenderDrawColor( renderer, 0, 0, 0, 0 );
+	SDL_RenderClear( renderer );
+	SDL_SetRenderDrawColor(renderer, 0xFF, 0xB0, 0, 255 );
+
+	int x = 0;
+	int y = 0;
+	for( int c = 0; c < 2 * 1024; c++ ) {
+		int v = buf[c] & 0x00ff;
+		for( int b = 0; b < 8; b++ ) {
+			if( v & 0x01 ) {
+				SDL_RenderDrawPoint( renderer, x, y );
+			}
+			v >>= 1;
+			x++;
+		}
+		x -= 8;
+		y += 1;
+		if( ( (c+1) % 128 ) == 0 ) {
+			x += 10;
+			y = 0;
+		}
+	}
+
+	SDL_RenderPresent( renderer );
+
+	int done = 0;
+	while( !done ) {
+		SDL_Event event;
+		SDL_PollEvent( &event );
+		switch( event.type ) {
+			case SDL_QUIT:
+			case SDL_KEYDOWN:
+				done = 1;
+				break;
+		}
+	}
+
+
+	SDL_DestroyRenderer( renderer );
+	SDL_DestroyWindow( window );
+	SDL_Quit( );
+
+	free( buf );
+	fclose( f );
+	return 0;
+}
+```
+
+And indeed I get:
+
+{{< figure src="/images/hardware/imc-2001/chargen.png" alt="character in the 40-char ROM" >}}
diff --git a/content/hardware/imc-2001-firmware.md b/content/hardware/imc-2001-firmware.md
new file mode 100644
index 0000000..b29aa8a
--- /dev/null
+++ b/content/hardware/imc-2001-firmware.md
@@ -0,0 +1,144 @@
++++
+title = "IMC-2001 Firmware"
++++
+
+# Intro
+
+The ROM consists of two ROM chips. The bigger chip labelled "ROM1" was
+broken (it got really hot) and could not be read (it returned all zeroes).
+It has no markings on it, so one can only guess it is something AT28C256
+compatible.
+
+The ROMs sit in the special "slot 0". The board has two other
+unused ROM sockets and an arrow pointing to an additional ROM socket on
+the motherboard itself.
+
+On the schematics the slot is not labelled "slot 0" but "ROM" and this
+gives away it's special purpose for the machine.
+
+# ROM 2
+
+ROM 2 (sticker with hand-written red 2 on top) is a Mitsubishi M5L2732K,
+32k-bit, 4k-ROM, seems very ok during operation (the carvings say
+"M5L2732K, 83080L, JAPAN").
+
+## lower-case patch
+
+Comparing ROM2 to the standard Apple autostart ROM 
+(https://6502disassembly.com/a2-rom/AutoF8ROM.html) we see only one difference at:
+
+```
+FD80 (F800+580)
+
+AutoF8ROM
+00000580  90 02 29 df 9d 00 02 c9  8d d0 b2 20 9c fc a9 8d  |..)........ ....|
+monitor.rom:
+00000580  90 02 ea ea 9d 00 02 c9  8d d0 b2 20 9c fc a9 8d  |........... ....|
+```
+
+```
+fd80: 90 02                    bcc     ADDINP
+fd82: 29 df                    and     #$df            ;shift to upper case
+fd84: 9d 00 02     ADDINP      sta     IN,x
+fd87: c9 8d                    cmp     #$8d
+fd89: d0 b2                    bne     NOTCR
+fd8b: 20 9c fc     CROUT1      jsr     CLREOL
+fd8e: a9 8d        CROUT       lda     #$8d
+fd90: d0 5b                    bne     COUT
+```
+
+*EA EA* are 2 nops where the *and #$df* is. This seems to do away with
+uppercasing the byte coming from the keyboard, so that lower-case character
+work.
+
+# ROM 1
+
+ROM 1 is hard to guess, what it originally contained (as mine got fried).
+
+# addressing mode
+
+I put back the original Autostart ROM, the addressing on the PCB is a little
+bit weird. As the monitor was working I could write a test ROM with
+
+```
+#!/usr/bin/tcc -run -Werror
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int main( int argc, char *argv[] )
+{
+        FILE *f = fopen( "./pattern.rom", "w" );
+        char *buf = malloc( 1024 );
+        for( int i = 0; i < 32; i++ ) {
+                memset( buf, i, 1024 );
+                fwrite( buf, 1024, 1, f );
+        }
+        fclose( f );
+        free( buf );
+        return 0;
+}
+```
+
+and get the following pattern in the monitor:
+
+```
+D000 1C
+D400 1D
+D800 1E
+DC00 1F
+E000 18
+E400 19
+E800 1A
+EC00 1B
+```
+
+So the replacement AT28C256 is arranged as follows:
+
+```
+0x6000 18 must contain the second 4k of the apple rom starting with e000 (24k)
+0x7000 1c must contain the first 4k of the apple rom d000
+```
+
+So I ended up doing this:
+
+```
+dd if=/dev/zero of=zero1 bs=1 count=24576
+dd if=Applesoft of=apple1 bs=1 skip=4096 count=4096
+dd if=Applesoft of=apple2 bs=1 count=4096
+cat zero1 apple1 apple2 > newrom1.rom
+```
+
+## Unkown difference
+
+When I watched the series on the Apple clone from Adrian's Digital Basement
+(he has a nice 3 part mini-series on the fixing of an Apple clone of unknown
+origin) I noticed the following difference:
+
+ROMS he published 'Apple\ II\ Clone\ ROM\ E0\ 300854cc.bin' which
+has one single difference in the E000 ROM:
+
+```
+                   ; Convert FAC to integer.  Must be -32767 <= FAC <= 32767.
+e10c: a5 9d        AYINT           lda     FAC               ;exponent of value in FAC
+e10e: c9 90                        cmp     #$90              ;abs(value) < 32768?
+e110: 90 09                        bcc     MI2               ;yes, okay for integer
+e112: a9 fe                        lda     #<NEG32768        ;no; next few lines are supposed
+e114: a0 e0                        ldy     #>NEG32768        ;to allow -32768 ($8000), but do not!
+e116: 20 b2 eb                     jsr     FCOMP             ;because compared to -32768.00049
+                   ; <<< BUG: A=-32768.00049:A%=A is accepted, but PRINT A,A% shows that A=-
+                   ; 32768.0005 (ok), A%=32767 (wrong!) >>>
+```
+
+instead of *a0e0* it has *a0e5*
+
+```
+                   ; <<< meant to be -32768, which would be 9080000000 >>>
+                   ; <<< 1 byte short, so picks up $20 from next instruction >>>
+e0fe: 90 80 00 00  NEG32768        .bulk   $90,$80,$00,$00   ;-32768.00049 in floating point
+```
+
+maybe the variable got moved to *e5fe* for some reasons? hard to tell, especially
+as the other ROMs have no differences. I kept mine on the original autostart ROM.
+
diff --git a/content/hardware/imc-2001.md b/content/hardware/imc-2001.md
index 54de32d..2abdabe 100644
--- a/content/hardware/imc-2001.md
+++ b/content/hardware/imc-2001.md
@@ -245,6 +245,11 @@ On the keyboard PCB there is a strange white connector with the following layout
 
 # Links
 
+## Subtopics
+
+- [Chargen40](/hardware/imc-2001-chargen40): 40-column character mode
+- [Firmware](/hardware/imc-2001-firmware): the monitor, Applesoft ROMs
+
 ## Other IMC-2001
 
 * [Mention of the IMC-2001](http://www.epocalc.net/php/liste_models.php?texte=&look=All+fields&yearmax=2018&nocomp=pc&cat=Apple+2+clone):