Great, we can switch to a graphics mode and even draw a colored pixel on the screen! But we've drawn at (0,0), the top-left corner – the easiest possible location. How do we draw at other locations? You'd expect the video memory to be organized linearly,
Now we're going to try plotting our first pixel! This is actually pretty straightforward, but it took LOTS of reading to initially wrap my head around it. My main reference is THE reference: The IBM PCjr Technical Reference, that is. It can be a little dense, so I
We're going to make our first foray into graphics by changing the video mode! There's lots of new stuff here – let's just jump right into it: [cpu 8086] [org 100h] jmp main %include 'formatting.asm' %include 'stdio.mac' main: ; Get
In a modern language we'd structure our code into methods and classes and organize it into different files to keep it from becoming overwhelming. We can do a little of that in ASM. The instructions CALL and RET support constructs called "procedures" - a labeled block
Let's look at our "Hello, PCjr!" code from Episode 1: [cpu 8086] [org 100h] mov dx, str_msg mov ah, 9h int 21h mov ax, 4c00h int 21h str_msg: db 'Hello, PCjr!', 0ah, 0dh, '$' Going line-by-line: 1. Tell NASM we'
That old PCjr I cut my coding teeth on 25 years ago is still with us, and presumably still in perfect working order, boxed up in my parents' basement. In addition, an original IBM PC model 5150 is boxed up in the attic, given to me by my father-in-law
Recently I experienced a huge wave of nostalgia for my first computer, the IBM PCjr. This image is forever burned into my mind: Or rather, something similar to this, because ours had several "sidecar" expansion packs bolted onto the side to increase the memory to 384KB, and it