(c)1990 Golden Triangle, Inc. (c)1990 Wilson Van Alst All rights reserved. Fm: Joe Sonneman To: Wilson Van Alst VAN--please explain more about scrolling rate limit on M100. Does this mean, if you use an external 2400 bps modem, that the effective speed is 650 bps? How can one download/upload at 2400 and read the download later, at leisure, off-line? Thanks, Joe - 0 - Fm: Wilson Van Alst To: Joe Sonneman You got it. The incoming data rate maxes at about 650 Baud unless you disable scrolling on the M100/102, no matter what your modem is capable of. What happens, in simple terms is: when the laptops feels the urge to print a new line at the bottom of the screen, it sends a ^S to the host computer, which stops transmission. Then the screen does its scroll routine, moving a bunch of characters inside the memory allocated to the 'Prev' screen and the normal screen, re-painting the normal screen, clearing the bottom line, and finally sending a ^Q to the host to start receiving and displaying the incoming data once again. The time needed for all that work is no problem at 300 Baud, but it becomes a bottleneck when you're dealing with 1200 or 2400 bps. So, how to disable scrolling? This program, run from the main menu, will take you into TELCOM with scrolling disabled: 0 'SCROFF.BA (c)1989 Wilson Van Alst 1 printchr$(27)"V"chr$(27)"T";:call21069 Operating in the scroll-off mode takes some getting used to; but it does allow you to download stuff at a true 2400 bps. BTW, the scroll speed isn't an issue for files you're uploading from the M100, because they don't display on the screen. - 0 - Fm: Bill Boyd To: Wilson Van Alst Your explanation of XON/XOFF was correct enough to be "in simple terms," but it does not describe what happens inside the computer accurately. In case someone wants to know, the printing to the screen and the reception from the host are independent. The main task the computer is doing is checking whether any characters are in the receive buffer, and acting on what it finds there. When a character comes in from the host, the computer puts it in the receive buffer, if it is not full. When the receive buffer is nearly full, it sends an XOFF (^S) to the host. When it has nearly emptied the receive buffer, it sends an XON (^Q) to the host. From the point of view of the main program the computer is running, these characters are showing up in the receive buffer out of nowhere. Thought someone might like to know the details. - 0 - Fm: Wilson Van Alst To: Bill Boyd What you describe concerning the role of the receive buffer is quite accurate -- and certainly comes closer to what's really happening than my oversimplified analysis. I can't quite agree, though, with your conclusion that "the printing to the screen and the reception from the host are independent." Let's see if this is comports with your understanding: As the computer plods through its routines for displaying characters on the screen, it temporarily stops "fetching" bytes from the receive buffer -- although new bytes may be arriving and accumulating there, thanks to the special "interrupt" status enjoyed by the RS232/modem port. If the screen display routine is relatively slow (eg., when the LCD needs to scroll a line), or the incoming comm data is relatively fast (eg., 650+ Baud), characters start to pile up in the receive buffer -- because they're not being "fetched" as quickly as they come in. If the slow LCD routines allow the receive buffer to get nearly full, the computer sends an XOFF to the host ... etc. 'Zat make sense? The ^S/^Q is, as you say, a function of the receive buffer's "fullness" -- but the latter is a product of (relatively) slow LCD display, especially when the computer has to sling all those bytes around during a scroll maneuver. - 0 - Fm: Bill Boyd To: Wilson Van Alst Yes, your explanation of the workings of the serial communications in conjunction with the display routines agrees with my understanding of how it works. As I said, they are independent (maybe I should have said "they are handled independently"), but, as you said, the receive buffer's "fullness" depends on how quickly the characters are displayed relative to how quickly they come in. Starting message #: 191143 Starting date: 06-Dec-89 01:15:57 Participants: Joe Sonneman 73760,717 Wilson Van Alst 76576,2735 Bill Boyd 75715,70