Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!ames!oliveb!slif From: slif@oliveb.UUCP Newsgroups: comp.sys.ibm.pc Subject: Re: Screen Scroll Speed on ATT6300 Message-ID: <750@oliveb.UUCP> Date: Wed, 1-Apr-87 16:55:46 EST Article-I.D.: oliveb.750 Posted: Wed Apr 1 16:55:46 1987 Date-Received: Sat, 4-Apr-87 09:20:59 EST Organization: Olivetti ATC; Cupertino, Ca Lines: 39 Keywords: flow control with medium speed serial interface Jean-Pierre Dumas writes: > Can anybody help/give a solution/explain why the scroll speed > on my Olivetti M24 (AT&T 6300) is at least 4 times slower than > on a IBM PC ??? Unlike the IBM BIOS, the 6300 BIOS writes to the display only during horizontal and vertical blanking times. This gives a flicker-free and snow-free display. However, this means that screen updates will be slower on the 6300 than on true blue. Also, since the 6300 uses a display which has TWICE the number of lines, there is less blanking time available. When operating the serial interface at greater than 1200 "baud", and also scrolling the screen, the characters are coming in faster than they can be displayed. If there is no buffering of characters received, the display updates will eventually cause the loss of characters. When scrolling occurs, there is not enough time to move (79 * 25 * 2) bytes in video memory, and keep up with the one-byte deep FIFO on the 8250 serial interface chip. Thus, if there is no flow control available, characters will be lost if the display is being scrolled at the same time. The solution is to NOT scroll the display during high speed transmissions, or to enable flow control of some sort, whether by XON/XOFF characters, or RTS/CTS RS-232 interface signals. I use KERMIT with XON/XOFF flow control at 9600 "baud" with no loss of characters. The display is clean, no flicker, no snow, and much easier to read than the "standard". Have you tried RTS/CTS flow control ? If KERMIT doesn't supply this [woops! ignorance showing], a serial interrupt routine may need to be written. If you MUST run the screen capture mode of KERMIT, and no flow control is available, you MUST run the serial interface at 1200 baud. Good luck solving the problem !