Kiwi's Blog - Learning and working in Assembly

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If I wanted to get bankswitching and sound working, then assembly would solve these 2 issues. Therefore, I need to start learning that.

 

The C functions and the BIOS call function are very close what they do. Such as fill_vram, and etc. I do have the Colecovision programming, ZiLog z80, and tms9918a information on hand.

 

I started on Saturday, and I was all worn out from working very hard from that morning. Fairly lousy day, and I wasn't feeling so well. So I decided just read about the z80 and http://www.z80.info/lesson1.htm did really good job explaining how the chip works. At least I know what the registers are for and how I may use them. I took a nap and realize how similar the actual C function in the getput/coleco library and the bios function. To use fill_vram in C, it's

 

fill_vram(0x2000,0x20,1024);color table, change the half of the color table to dark green with black background.

 

In assembly, I thought in my mind what if,

ld a,0x20 (data)

ld hl,0x2000 (possibly where to load the data to color table)

ld de,1024 (count how time to do this)

call FILL_VRAM

 

So, that thought process made me try playing with assembly today. So I thought of how about I try to load my pattern, name, and color table. That was my very first objective that I did with my C programming project.

 

I used the Helloworld assembly example since that file compiles. I managed to load my tiles and such with

xor a

ld hl,PATTERN

ld de,$0000

ld bc,2048

call WRITE_VRAM

 

same with the name table and the color table. The color table was set at 32 group of colors. So 'call MODE_1' will set up the screen for you from it preset of vdp registers. Therefore, the screen is set on screen mode 0. So I need to set the screen to screen mode 2. I searched for the tms9918a and set up the registers. I do so by,

 

 

ld b,0

ld c,%00000010

call WRITE_REGISTER

ld b,1

ld c,%11000010

call WRITE_REGISTER

ld b,2

ld c,$06;name 1800

call WRITE_REGISTER

ld b,3

ld c,$9f;color table 2000

call WRITE_REGISTER

ld b,4

ld c,$3;pattern generator 0000

call WRITE_REGISTER

ld b,5

ld c,$36;1b00

call WRITE_REGISTER

ld b,6

ld c,$07;sprites

call WRITE_REGISTER

ld b,7

ld c,$F2

call WRITE_REGISTER

 

This should work the same as Screen_mode_2_text function, where you have to load the pattern table to $0800 and $1000 to get around the sprite cloning issue. I don't have the interrupt bit on, but I think it need to stay off until the data is loaded to VRAM, then flip the interrupt on when the game is playing. I think rle compression probably use fill_vram, but that's worth building a function in my program.

 

I'm excited to gain some ground with this language. I will be experiment with the sound since the bios sound set up looks similar to C programming set up. It need the address of the table of sounds on ROM so it'll load the 16 bit value to address 7020. Then PLAY_IT.

 

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