Posted By
JamesD
on 2017-02-15
16:18:18
|  Re: A mathematical demo
I told you what that means.
This is from a CoCo page, but the Dragon is basically a clone of the CoCo. This is controlled by a chip called SAM, Synchronous Address Multiplexer. aka the MC6883
"POKE 65495,0
doubles speed of ROMs; Basic programs by 1 and a half. Does not work with all computers, or with disk, cassette or printer operations."
RAM is still at .89 MHz
The behavior is mentioned on page 11 of the datasheet.
The machine starts up in "Slow" mode.
The POKE enables the A.D. (address dependent) mode where high speed is enabled for ROM.
There is "Fast" 1.7 MHz mode, but it disables DRAM refresh and display updates.
In Fast mode, the machine locks up within seconds unless you modify it to have SRAM instead of DRAM... something I've never seen anyone do.
The CoCo 3 can run at a full 1.7 MHz since it's based on a gate array designed to do it.
Unless the benchmark was performed on a CoCo 3, it wasn't a full 1.7 MHz
You can find the data sheet here:
https://ia801708.us.archive.org/22/items/Motorola_MC6883_Synchronous_Address_Multiplexer_Advance_Sheet_19xx_Motorola/Motorola_MC6883_Synchronous_Address_Multiplexer_Advance_Sheet_19xx_Motorola.pdf
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