Epson MX-80 User Manual page 40

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Chapter 9

Oops! What went wrong here? We sent the same ASCII number to both the

^'—'computer and the Printer, but the results are different. The screen shows

Figure 4-1

while the Printer says

Figure 4-2

Some explanation is in order here, and it better be good!

WELL, AHHH,

ER,

UMMM

It's like this.

By tradition, ASCII code numbers 0 through 31 are reserved for control codes.

It is in this area that different computer makers do their own thing, sometimes

agreeing on little else than # 7 should be reserved for the BELL (buzzer). The

Model I is also a "free spirit".

By further tradition (but less deeply steeped), ASCII numbers 128 through 159

are reserved for those same control codes, more or less. In the case of the Model I

— more. In fact, the Model I control codes found between ASCII 128-159 are

more complete than those found between ASCII 0-31. Terrific! We really needed

that, didn't we.

But What Does It All Mean?

It means that the upper set (higher numbers) of control codes is better than the

lower set, that's what it means. In order to get the maximum capability from the

Model I, we have to use the upper set of control codes.

The problem is, the TRS-80 Model I uses those same upper ASCII numbers inside

the computer to put graphics characters on the screen. When they are sent outside

the computer via LPRINT, they are properly interpreted as control codes. EPSON

had to move the graphics characters up out of the way and give them new ASCII

numbers.

Who's Responsible For This Mess?

Now, now. There'll be no finger pointing. However, if it wasn't screwed up to

start with, EPSON wouldn't have had to take evasive action to fix it.