7470A Plotter and the 41

[4ster]

I've been using the Plotter Module exclusively and not really delved into using HPGL commands not available on the Module. I am working through the "Interfacing and Programing Manual" for the plotter, and am just now realizing that I can access more functions than the limited set on the Plotter Module.

The manual only has one example of sending the plotter HPGL over HP-IL using the 41. I am confused over a few of lines in that program. Most (maybe all) HPGL commands require a terminator, commonly ETX - ASCII decimal 3. I gather Lines 13 through 18 below send the ETX terminator.

The manual's example of an HP-41 program follows:
01 LBL "CTP"
02 AUTOIO
03 FIX 0
04 CF 29
05 2000
06 "SP1 PA1000,"
07 ARCL X
08 OUTA
09 41
10 "LBHP "
11 ARCL X
12"^ SENDING DATA"
13 0
14 ENTER
15 3
16 BLDSPEC
17 ARCL X
18 OUTA
19 "SP0"
20 OUTA
21 END

The plotter plots: "HP 41 SENDING DATA" and puts pen 1 back in it's storage position.

I've never encountered BLDSPEC used in this way. I've always assumed it was only for creating special characters for the printer. How does it work to create an ETX in HPGL?

[Mark Hardman]

From page 330 of Extend Your HP-41 by W.A.C. Mier-Jedrzejowicz, Ph.D.:

Quote:You can use BLDSPEC to create display characters not available from the Alpha keyboard; use CLX, ENTER - then put the character number, 0 to 127, into X and execute BLDSPEC. You can store this character or put it into the Alpha register by using ARCL. This method was used before synthetic methods or the Extended function XTOA were available. For byte values greater than 127, use CLX, ENTER, 1, BLDSPEC, c-128, BLDSPEC, where c is the character number.

HTH

Mark

[4ster]

That helps a lot, thanks. It also gives me some better alternatives.