standish@mentor.cc.purdue.edu (Dreamwalker) (12/02/90)
Could someone tell me what the baud rate divisors are for a modem? I'm having no luck in trying to hack them out from trial and error. Basically, I am writing a terminal emulator, and need to know what the divisor words are for the baud rate generator, where the low and high bytes are writen into ports 03F8h and 03F9h, respectiely. All I have is that 300 baud is 384, and operating at 300 baud these days is torment for any normal hacker. Any help will be much appreciated. Dreamwalker
hughes@locusts.Berkeley.EDU (Eric Hughes) (12/02/90)
In article <2128@mentor.cc.purdue.edu> standish@mentor.cc.purdue.edu (Dreamwalker) writes: >Could someone tell me what the baud rate divisors are for a modem? You are really programming the serial port chip, not the modem. >All I have is that 300 baud is 384, ... A baud rate divisor takes an external clock and divides it down to get lower frequencies. Thus if 300 bps corresponds to 384, then 1200 bps corresponds to 384/4 = 96, 2400 bps --> 48, 9600 bps --> 24, and 115200 bps --> 1. This is where that 115 Kbps figure for fast serial port connections from PC to PC comes from. Eric Hughes hughes@ocf.berkeley.edu
everett@hpcvra.cv.hp.com.CV.HP.COM (Everett Kaser) (12/04/90)
According to my notes, you're right that the baud rate divisor for 300 baud
is 384. My understanding is that in order to double the baud rate, you simply
halve the baud rate divisor. Hence:
BAUD DIVISOR
75 1536
150 768
300 384
600 192
1200 96
2400 48
4800 24
9600 12
19200 6
38400 3
57600 2
115200 1
Best of luck.
Everett Kaser Hewlett-Packard Company
...hplabs!hp-pcd!everett work: (503) 750-3569 Corvallis, Oregon
everett%hpcvra@hplabs.hp.com home: (503) 928-5259 Albany, Oregondougs@videovax.tv.tek.com (Doug Stevens) (12/05/90)
In article <31600010@hpcvra.cv.hp.com.CV.HP.COM>, everett@hpcvra.cv.hp.com.CV.HP.COM (Everett Kaser) writes: > My understanding is that in order to double the baud rate, you simply > halve the baud rate divisor. Hence: > BAUD DIVISOR > ... > 115200 1 > Some manufacturers do not guarantee their parts to operate with a divisor of 1. National Semiconductors does not list it as an option (although, in practice, it does work).