wtm@neoucom.UUCP (Bill Mayhew) (08/21/89)
Hi, I am working on a package that needs to run on a Tandy 1400LT portable computer. The computer will be in place where AC power is available, so battery life is not a concern, but portablility of the machine is needed (hence we're not using a desk-top machine). What is causing me a bit of a problem is that the 1400LT has a built-in sleep mode that activates after a user-selectable time of 1 to 179 minutes. Unfortuantely, there is no documented way to disable the sleep mode. I am looking for widely separated events that come in over the COM1: port, so the machine may need to be up for more than the nominal 179 minutes. Apparently, the BIOS INT09H (keyboard) call resets a time-out somewhere, so that as long as there is periodic keybaord activity, the machine will stay on. Keyboard activity also will wake up the machine. Curiously, INT10H (video services request) appears not to be hooked. I've been going through the BIOS digging around, and INT09H (the hardware timer tick) and INT1CH (user callable timer tick) are apparently NOT used to decrement the time remaining until sleep!! There are some interrupt vectors that would normally go the the second 8259 on an AT machine that are in use on the 1400LT, but I haven't been able to figure them out yet. I dug around in the Tandy hardware refence manual, and haven't been able to come up with anything definitive. The documentation on the BIOS is extremely limited. I did notice in the schematics that there is a square wave output from the real-time battery back-up clock to one of the PAL chips, so I am beginning to suspect that the sleep mode is actually controlled by a register in the PAL, rather than the BIOS. Booo!, if that's the case. By the way, one of the benefits of the sleep mode is to extend the lifetime of the lead sulfide backlight panel for the display. In all portables (with the exception of ones that use fluorescent tubes [Zenith Supersprot, e.g.]) the backlight has a fairly limited life. The backlight reduces to about 50% of its original intensity after about 2000 hours (about 2 years of average use). Obvisouly, switching off the backlight when it is not needed is a good thing to do. In the case of the 1400LT, it is possible to shut off the backlight without going into sleep mode. I wrote a little TSR program that traps INT08H, INT09H, and INT10H to shut off the backlight after a user-selectable period of inactivity without going into sleep mode. This is useful where you have a time-intensive application where the CPU needs to keep going, but you don't really care about viewing the display. I'll see if I can send the backlight TSR to one of the source groups (the executable is about 300 bytes). IF you want to experiment yourself, the backlight is controlled by bit 3 in port 0FAH. Witing a 1 into that bit turns the backlight on, while a 0 shuts it off. Right now, I have 50% of my problem is solved; I can save the backlight, but I can't avoid going to sleep. Thanks to anybody that can help. Bill email: wtm@impulse.UUCP or wtm@neoucom.edu Bill Mayhew Division of Basic Medical Sciences M-117 Northeastern Ohio Universities' College of Medicine Rootstown, OH 44272-9995 USA phone: 216 325-2511