6809 Assembly programming for the Fujitsu FM-7

The FM-7 is one of a series of Fujitsu computers released in Japan With a pair of 6809 CPU's it was widely popular in Japan, and is one of the few 6809 computers released. In these tutorials we'll learn the about the FM7, and write some simple programs for it

FM-7 Cpu Main: 2mhz 6809 Sub:  2mhz 6809 for GPU Ram 64k Ram 48k VRam Sound AY-3-8912 optional FM2203 add on Max Resolution 640 x 200 @ 8 colors (RGB CMY BW)

ChibiAkumas FM7 Tutorials

Useful Documentation

FM-TechKnow (FM7 FM77)

FM7 New7 77 Assembly Introduction

Hello World Example

Here is a sample file... We've provided a Header, containing the Length and destination load address... There is also an Exec address in the footer, however this does not actually have any effect! The hello world example uses the PrintChar routine in the basic rom at $D08E of the FM-7 OS

StartUp File

To make our disk automatically start, we need a basic launcher. Here we've written a BAS file, it will load machine code program "PROG" (which has a built in destination address of &H2000) Next we execute it with an EXEC command We need to save this as "STARTUP" (Case Sensitive)

Building our program to the disk

We need to create a binary file (with a 2b0 extension) We use ASW to compile the program, and P2Bin to convert it to a binary. To add a file to a disk we'll need the Ftools kit We'll use a template disk (with our STARTUP bas) and attach the 2b0 file to it

Sending Data to the Sub CPU

The Sub CPU handles graphics drawing and key input - it's a second 6809 To control it we have to send data to it via a 128 byte shared memory block, between $FC80-FCFF ($D380-D3FF on the Sub CPU side) To do this, we have to: 1. Wait for the Sub Cpu to not be busy (wait for Bit7 in $FD05 to equal 0) 2. Halt the Sub Cpu (set Bit 7 of $FD05 to 1) 3. Copy command data to $FC80-FCFF 4. Resume the Sub CPU (write 0 to $FD05) The command will then be processed by the sub CPU

if we HALT and RESUME the sub cpu but don't set a command there WILL be trouble! When we do this we need to set the 'request ready' bit (Bit 7 of $F780) - this will stop the SUB CPU trying to process a command and getting confused.

RAM Main CPU

** $FD0F Enable/Disable Basic ROM 8000-FC00 (Write=Disable... Read= Enable)

RAM Sub CPU

Ports on the Main CPU

Ports on the Sub CPU

Colors

Char Map

FM77 4096 color mode

The FM77 adds lots of new functionality, The best of which is 4096 color mode and the MMU!

4096 color mode allows us to use a 320x200 screen with up to 4096 colors, meaning each pixel is define by 12 bits. this means the whole screen is a huge 96K! The MMU is a 'Memory Mapping Unit', which allows us to map the 64k of addressable 6809 memory space to any part of the physical  memory. The major benefit of this is that we can now access the VRAM without the Sub CPU! The FM77 allows for 'Page flipping' so usually two screen banks can be toggled, with one visible and the other drawn, however in 4096 color mode, these two must be used, as Page 0 contain the bit 3,2 of each color channel, and page 1 contains bit 1,0.

Writing 96k of video memory would be a real pain, but if we only want a small number of colors, we can only use a few bitplanes, and simply 'redefine' the palette, so we can use the lowest bits of Blue and Red (B1,B0,R1,R0) giving us 4 bitplanes for a palette of 16 colors out of the total 4096, or even 6 bitplanes for 64 colors, massively reducing the amount of data transferred, while giving us impressive color capabilities for an 8 bit system!

Color number bits when setting palette (0-4095):
%0 0 0 0 G3 G2 G1 G0 R3 R2 R1 R0 B3 B2 B1 B0

FM77 Memory mapper

Before using the memory mapper we need to enable it by setting bit 7 of $FD93 (Write $80)

It should be noted that while the memory can be mapped to any of the 16 4k blocks from $0000-$FFFF, the $FC00-$FFFF actually never changes, and is always mapped to the default hardware registers for the main CPU

However this gives us a great opportunity! By writing $1D to $FD8F (the MMU register for $F000-$FFFF) we can 'switch in' the hardware registers of the SUB CPU ( usually found at $D400-$D7FF on the SUB CPU) - This allows the MAIN cpu to access these registers in the range $F400-$F7FF , meaning the $F000-$FFFF range can now be used to access all hardware IO for the MAIN or SUB CPU!!!

Special Chars

Graphics Operations

Commands that can be sent to the Sub CPU

There are a variety of commands that can be sent to the Sub CPU, there are some special 'secret' ones called the YAMAUCHI calls (Also know as TEST commands),
These allow data to be direct copied to the SubCPU and allows for execution

The FM8 required $3F to be followed with the 8 byte 'YAMAUCHI' string... but FM7 onwards didn't check it ... There still needs to be 8 bytes 'there' before $9x commands - but they can be anything.

AY Registers

FM Registers

Joystick Reading