Sprinter II. (evaluation) Bruce Powel Douglass.
In my work as a neurophysiologist, I designed a simulation of a nervous network to run on a microcomputer. The only trouble was, to get a statistically significant sample of output from the simulation, I had to run the model for 2 1/2 days on our HP-85. Something had to be done!
Actually, more than one thing. These things included changing from an HP-85 to a TRS-80, rewriting the simulation in a compiled language (Alcor Pascal), and increasing the speed of my computer. But which modification to use? Points of concern were:
1. How easy is the modification to make?
2. How much speed increase will there be?
3. Will it actually deliver?
4. Will it work under all the conditions necessary to gather and analyze the data?
After looking at the options available, I made what appeared to be the best choice, Holmes Engineering's Sprinter II.
Sprinter II, which lists for $99, is the fastest speed up modification for the TRS-80 Model I and III currently available. It is also the easiest to install and one of the least expensive. The Sprinter II gives you 16 different speeds from which to choose, all integer multiples or dividends of the standard 1.77 MHz clock speed. For Model I machines without an expansion interface, an optional printer port can be provided as well for an additional $24. Since I have a disk system, I did not need the printer port.
The installation of the Sprinter II was certainly one of the less traumatic surgeries my TRS-80 has undergone in its short life. First, you remove the cover of the keyboard, and (carefully!) remove the Z80 chip from its socket. A flat screwdriver works well for this. Then, you take the Holmes Sprinter II (which has its own Z80B processor in it) and plug it into the empty Z80 socket. Four wires with special solderless clips are placed on specific pins on different chips (no soldering at all need be done). Then you reassemble your computer and the job is done. Life should be so simple.
The modification just described will work on all machines, but depending on the components, you may not see your machine running at 5.3 MHz. As the manual says, "All TRS-80s were not created equal.' There are many reasons why your machine may not run as is at 5.3 MHz. Most computers will run at a clock speed that is less than 5.3 MHz, but nevertheless faster than the normal 1.77 MHz.
For example, some TRS-80s were made with RAM chips that run at 450 ns rather than the current standard of 200 ns or 150 ns. You may have to replace these to run your TRS-80 at three times normal speed. Or, you may have to solder 1K resistors to avoid loading the RAM chips, etc. However, the manual states that in all cases, the manufacturer has been able to get a TRS-80 to run at 5.3 MHz with extra wait states for memory access. If worse comes to worse, you can send your keyboard unit to them, and they will make the installation for you and charge you for the parts and labor necessary for modifications they will have to make to get the machine working at 5.3 MHz. The manual describes a number of fixes for machines that won't run at top speed.
My own experience was that installation of the Sprinter II enabled the machine to run at twice normal speed, but it just wouldn't run at three times normal speed. I talked to the helpful engineers at Holmes and discussed my problems. We decided that the modifications necessary to get it working at three times normal speed (5.3 MHz) were beyond my admittedly meager soldering abilities, and I packed my keyboard off to them to make the modifications (I really wanted to get it running at 5.3 MHz!). The service bill was a modest $60 for labor and parts--a most worthwhile investment.
The installation manual is clear and concise. It has photographs to show exactly where the solderless clips should be attached, and which trace to cut in an optional modification that really ought to be made. The manual explains how to take the cover off the computer and how to put the screws back in when you are done. The most inexperienced hacker should be able to follow the manual without error.
The troubleshooting guide describes common problems and solutions. These all refer to errors you may have made in the installation procedure or to particular parts in your system that may be failing at high speed. The manual also describes some optional modifications to disable the automatic changes back to normal speed during cassette or disk I/O. The Sprinter II automatically returns to normal speed when oen of these operations takes place, and then returns to its previous speed when the I/O is completed. These optional changes allow you to run high-speed tapes, and double density 8 floppy disk drives. The unmodified TRS-80 cannot operate an 8 drive.
Running The High Speed Mod
Controlling the clock speed couldn't be easier. The control for clock speed is all software. The BASIC OUT 254X statement is used to adjust the speed anywhere from 1/3 normal speed to three times normal speed. Your TRS-80 may not work at some of these speeds for the reasons mentioned above. A little experimentation will show you which is the fastest speed for your machine.
Machine language can also be used to control speed. Sonce TRS-80 DOSes don't allow an OUT from DOS, I wrote the simple assembly language program, Fast, shown in Listing 1.
Fast is a simple program that executes automatically at a system boot. It outputs a 12 to port 254, displays a message to that effect, and then returns to DOS. I wrote another program called Slow, which returns the machine to the normal 1.77 MHz clock speed by sending a 0 to the port (it hasn't been used yet). Using the Sprinter II is that simple.
Although initially I could get my TRS-80 to run at only twice normal speed, Holmes Engineering installed the necessary modifications to enable it to run at 5.3 MHz with wait states added during memory access. I have used the modification without any problems whatsoever on any programs, including database management programs, compilers, statistical and other mathematical analysis programs, and programs to load neurological data from an external A/D converter connected to electrodes stuck in my pet leeches. I boot, my DOS automatically executes Fast, and I go (quickly) from there.
The biggest problem I have had with it is rewriting the timing loops in Basic and machine language programs because my TRS-80 is executing so fast. If you play games that play music, the music will, of course, be much faster. A simple fix for that would be to find the music output routine in memory and have it multiply the value for the tone length delay constant by the command of the increase in speed, and then execute the tone. For a machine running at twice normal speed, you shift the number left one bit, so it's quite easy to program.
If you find your TRS-80 a little slow starting in the morning, try a healthy dose of Sprinter from Holmes Engineering. It is an inexpensive but high quality modification that is truly easy to make and to use. By the way, my simulation now runs in 15 minutes.
Holmes Engineering, 3555 South 3200 West, Salt Lake City, UT 84119.
Table: Listing 1.
Photo: The Sprinter II from Holmes Engineering.
Products: Holmes Engineering Sprinter II (computer apparatus)