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Installing the Dallas Semiconductor DS1216E on the PCjr |
The DS1216E is a wonderful little chip that can add clock and calendar functions to your ancient machine. The instructions here are general instructions that can be applied to most older PCs and XT class machines, including the PCjr. The only thing specific to the PCjr about this page is the location of the correct system ROM to use, which is detailed below.
Introduction
Older PCs and XTs designed before the arrival of the PC AT generally did not have built-in clock and calendar function. You manually set the date and time each time you turned on the PC. Many add-in boards added a clock and calendar, but your system may not have such a board or the one it has may not be working.The Dallas Semiconductor 1216E chip can be used to add clock and calendar function to many old machines without requiring an add-in board. This is especially important for machines where an add-in board can not be located, or there is not space for one.
The DS 1216E is a hybrid chip. It contains a 28 pin DIP socket, a small chip and a battery. You install it underneath a 28 pin ROM chip, re-installing the ROM chip in the DIP socket provided by the DS 1216E. The price of the chip is steep, but it is worth it.
How it works
Normally you only read the date and time from a clock and calendar chip, which makes installing it in a ROM chip socket ideal. However, you do need to set the date and time occasionally. How is this accomplished when there is no circuitry to write data to the chip? (ROM chips can be read, but not written to, so motherboard circuitry generally doesn't allow for writes to ROM chips - it would be wasted.) Dallas has a neat trick to get around the fact that you are in a ROM socket. The DS 1216E constantly monitors the address lines going to the ROM chip. If a certain sequence is detected, the DS 1216E cuts the ROM chip off and starts to interpret the next part of the sequence. The effect is to use the address lines as data lines for programming the clock and calendar chip. After programming is complete, the DS 1216E re-connects the ROM chip and then begins to monitor the address lines for the next occurrence of the special sequence.The sequence is relative long - 64 bits worth on one of the address pins. The 64 bits are chosen such that they would never look like valid memory accesses. Your chances on tripping the DS 1216E accidentally are 2^64, which is quite unlikely.
Hardware Installation
This isn't a complete document that will hand-hold you through the process. If you are uncomfortable, find help.First, find a 28 pin ROM chip that the DS 1216E can be installed underneath. Most often this will be a BIOS chip on your motherboard. The DS 1216E will add some height so make sure that the original ROM chip will fit when it is reinstalled with the DS 1216E under it. (Plan for about one half inch of additional height.)
Although the DS 1216E will work in any location where software can 'wiggle' the address lines, the software that is included in this distribution is more specific. The software is designed for a ROM chip that starts at F000:0000 in the PC memory map. The ROM chip that the DS 1216E is designed to work with probably holds 32K of ROM, and the specific ROM chip you pick may not be at that exact address. Unless you want to fool with patching the software, you need to pick the ROM chip that responds to memory accesses at F000:000.
There are two ways to figure out which ROM chip to install the DS 1216E under:
- Brute force: Pick a ROM chip. Install the DS 1216E and hope the included software works. If it doesn't, either patch the software to work or uninstall and try again with a different ROM chip. Be careful, all of this stuff is delicate.
- Scientific: Find the technical reference manual for your motherboard and hope you can learn the correct ROM chip by finding it in the schematics.
Remove the ROM chip from the motherboard. Use an IC puller to avoid bending the pins, and take precautions against static. Remember the orientation of the chip - it will have a notch on one end.
Install the ROM chip in the socket on the DS 1216E. One end of the DS 1216E is notched, and that notch should line up with the notch of your ROM chip. Ensure that you do not accidently bend a pin the wrong way when installing.
Install the combined ROM chip/DS 1216E package back in the ROM chip socket on the motherboard. Mind the pins again ... you really don't want to find a replacement for a 20 year old ROM chip, do you?
Software Installation
Here is the link to DS1216E.ZIP.Boot the machine to DOS and run the TESTCLK.EXE program. This will ensure that the DS 1216E can be found and programmed.
Next, use the DOS software to set the current date and time on the DS 1216E chip, and add the software to your AUTOEXEC.BAT file. The program is called CLOCK.COM, and it does not stay resident in memory.
If you change the date and time using the DOS DATE and TIME commands, it will *not* update the DS1216E - you need to use CLOCK.COM to update the DS 1216E. However, you should not have to do this often.
An alternative design for the software would have been a device driver that stays resident and integrates with the DOS DATE and TIME commands. I generally don't like that approach, as you rarely want to set the date and time - you are more interested in reading it at bootup.
Credits
This file is my work. Nothing else is. I was tempted to write code to do this, but I was lucky enough to find some code that already worked and worked well. (Special thanks to 'RailDavid' for that code.) Zenith Data Systems is responsible for the provided
code. It
is
copyrighted code. They did *not* provide licensing information or embed
it in the comments of the provided source code. Be responsible - use
this, but remember where it came from and respect the copyright.
(C)opyright Michael B. Brutman, mbbrutman@yahoo.com
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