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The Earliest microbee Hack! - someone - 26-01-2022
The earliest known enthusiast microbee hack was a CPU turbo switch allowing it to be boosted from 2MHz to 4MHz.
It was done with kit microbees with the hack comprising of two switches, a PCB track cut, replacement of the Z80 CPU and PIO with 4MHz 'A' versions and replacement of the MWBASIC and FONT ROMs with 250ns versions.
Switch A (SPDT) was used to select the CPU speed of either 2 or 4MHz.
Switch B (SPDT momentary with centre off) was used to invoke the /WAIT signal momentarily prior to changing the position of Switch A.
When in boost mode programs ran twice as fast, however, with the tape, speaker and serial being bit bashed one needed to switch back to normal speed to use them.
RE: The Earliest microbee Hack! - mjelic - 23-02-2022
Is there any way to find out what speed your machine is running at? My 128k has the A versions of both CPU and PIO.
RE: The Earliest microbee Hack! - MbeeTech - 24-02-2022
(23-02-2022, 10:04 PM)mjelic Wrote: Is there any way to find out what speed your machine is running at? My 128k has the A versions of both CPU and PIO.
Quick answer : 3.375Mhz
All Microbees, apart from very early kit & production machines (1982) run at 3.375Mhz.
The only other exception is the early production of 256TC machines which were software switchable
between 3.375Mhz & 6.75Mhz. 6.75Mhz was unstable though, so support was removed.
Writing a routine to check approximate execution speed of the Microbee probably wouldn't be too hard
if you based it around detecting CRTC vertical retrace time that can be detected through the 6545 screen
controller registers.