Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!columbia!rutgers!husc6!endor!arena From: arena@endor.harvard.edu (Mike Arena) Newsgroups: comp.sys.ibm.pc Subject: Accessing COM2 from assembly language: Help Needed Message-ID: <985@husc6.UUCP> Date: Mon, 12-Jan-87 16:41:14 EST Article-I.D.: husc6.985 Posted: Mon Jan 12 16:41:14 1987 Date-Received: Tue, 13-Jan-87 00:45:56 EST Sender: news@husc6.UUCP Reply-To: arena@endor.UUCP (Mike Arena) Distribution: na Lines: 37 I have been trying to write a small terminal emulation program in assembly language by directly manipulating the serial port registers and taking over the communications interrupts. The serial port registers for COM1 are at 3F8-3FE. I use the OUT command to write directly to the transmit register. I Take over the interrupt 0C which monitors the Data Available Interrupt and captures characters asynchronously into a 1K buffer. I use the BIOS Interrupt 14 to initialize the comm port. This works great for COM1 even at 9600 baud. The problem is that I tried to make another version which would run on COM2. I changed all of the addresses for the serial port to 2F8-2FE (which is COM2) and still used interrupt 0C to capture incoming data. I also changed my call to INT 14 so that it initialized COM2 instead of COM1. So then I had an exact duplicate of the first program except that some addresses were changed and a few data bytes. The program could transmit data but not receive. I poked around in some other tiny comm programs (JaxTalk and TTalk, both just a few hunderd bytes) which I got off of a bulletin board and they used interrupt 0B instead of 0C to capture data for COM2. So I made the change but still no effect. In fact JaxTalk and TTalk did not work on COM2!!!! The computer I was using was a Compaq which might be the source of the problem but I doubt it since they are so compatible. I don't have access to a regular IBM PC with two comm ports so I don't know if it even works on that machine. If anyone has an idea what the problem is, please post an answer or mail to me at arena@harvard.harvard.edu. Michael J. Arena 316 Conant Hall 36 Oxford Street Harvard University Cambridge, MA 02138