Posted By
Litwr
on 2017-02-16
11:39:57
|  Re: A mathematical demo
Maybe Dragon and Tandy Color have some differences. I can give a citation from The Dragon 32 Dragon Companion by M.Jarvis.
"
PROCESSOR SPEEDS
Another feature of the Dragon which is very interesting, and indeed can be
extremely useful, is the fact that it has a variable processor clock rate. For those of
you who do not understand about clock rates a simple explanation is that the
central processing unit (in this case the 6809E) receives a regular tick from a timer
which tells it to move on to the next stage of obeying an instruction. These ticks
are measured in megahertz (millions of ticks per second) and the faster the tick the
laster the computer works. ln the Dragon's case the clock rate is controlled by
SAM bits in locations 65494 to 65497. These four locations control two SAM bits
which should give us four clock rates. Table 5 sets out the functions of the
locations.
...
Table 5.
Two bits should give four speeds but the Dragon appears only to respond to three.
The default speed, set on switching on, is the slowest with both SAM bits cleared
(poking any value to 65494 and 65496 achieves the same effect). The next faster
speed is set by poking to 65495 and results in the execution of programs being 50%
faster. The slowest two speeds are the only ones which can be used and still retain
video synchronisation.
The next increase in speed is achieved by setting bit 1 and clearing bit 0. Execution
speeds are 100% faster than the default speed but video synchronisation is lost.
This speed would be useful if a program involves large amounts of computation
and where video is not important. Video synchronisation can always be regained
by slowing the processor down again after the burst of computation.
The final speed should be achieved when both bits are set but as I have said, the
Dragon does not appear to respond (see the example program).
One thing to remember about the faster speeds is that the cassette interface will
only work at the default speed"
BTW the wikipage mentions 1.79 MHz, not 1.7
I agree that modern electronics is a kind of paradise...
|
