What Makes 486 Chips Work?
The Age
Tuesday November 28, 1995
COULD you please explain how the DX2 and DX4 486 chips work please. Is it true that the 486 DX4/100 is basically four DX25 chips, in the one chip?
-- S Curryman, Melbourne.
No, that is not true. The 486 chips have an internal clock speed, which is used by the CPU to process its instructions, and an external clock speed which is used to communicate with the rest of the world, consisting of the memory, controllers, video etcetera. The 486DX-100 is a clock tripled 33 Mhz 486.
It is a single CPU that operates internally at 100 Mhz and externally at 33 Mhz. The 486DX-66 is a 33 Mhz chip operating internally at 66 Mhz while the 486DX-50 is a clock doubled 25 Mhz chip. The letters DX indicate that an internal mathematical co-processor is present. This greatly improves the speed of mathematical calculations. but has little effect on Windows.
Which UART?
I HAVE a 28.8k modem but have had trouble getting connected to the Net. Apparently the problem is a UART chip. Mine is apparently 16450 and I need a 16550. Until I upgrade I must run the modem at 19.2k. Could you explain what UARTs are please? Is there any way I can run the modem at 28.8 k with a 16450 chip? G Hardy,Glen Waverley.
A UART (Universal Asynchronous Receiver / Transmitter) is the part of a serial port that takes character data, eight bits simultaneously, from the computer and converts it to serial data, sending out one bit at a time, and vice versa.
The main difference between the 16450 and 16550 chip is that the former has a one bit (not byte) buffer while the latter has a 16 bit buffer.
If you are running only DOS, the CPU doesn't have anything else to do but to devote all its attention to the serial port, so the 16450 will operate at 28.8 kbps and much higher.
Only under multitasking operating systems, such as Windows, is the 16550 needed, as the CPU is required to do other tasks while the data is being sent or received.
With a serial buffer, incoming data is not lost while other activities interrupt the CPU to do other tasks. If you use Windows you should buy the 16550 chip.
Regardless of the UART, your communications program should be set the to 38.4 kbps. The modem should communicate to the computer at a higher rate than to other modems because is you are using modem data compression, then the actual data when uncompressed will be higher than 28.8 kbps.
Stripping ASCII.
I HAVE received a file produced by an old wordprocessor which contains many funny characters such as a lower case "a" with an accent above it. I am using the DOS Editor to remove these when I find them but is there a method to remove them all?
D.Smith,Mooroolbark.
YOUR wordprocessor may be able to fix this for you in a simple step. Try loading the old file and save it as plan text. View this saved file and if is plain text then your problem is fixed.
If your wordprocessor cannot save it correctly, then is possible to use the DOS Editor to make global changes. The trick is to enter, via the keyboard, these funny characters.
This is done by holding down the Alt key and typing the three character ASCII code on the numeric keyboard.
Definitely not intuitive! To enter a lower case a with an accent above, the code is 160, a beta symbol is 225 and then select Change All and all will be gone.
You must obtain a listing of these ASCII codes. They are usually found in most DOS manuals.
If you would like your questions answered, fax them to George Skarbek on (03) 9601 2960 or write to him care of Computer Age, 250 Spencer Street, Melbourne, 3000. He can also be contacted via the Internet as gskarbek@melbpc.org.au).
© 1995 The Age
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