Factor of Matt

Report 1

DesTestMAX halts with garbled screen

Lee from the excellent More Fun Making It YouTube channel reported that DesTestMAX crashed with a corrupt screen while performing the 1K-2K test. Lee discovered that U25 (one of the rwo ram-address muliplexers) in his '64 was faulty.

Such a faulty mulixplexer will cause the wrong (possibly random) addresses in memory to be accessed instead of the one intended. DesTestMAX only uses two locations in memory during the 1K-2K test and it seems like one or both got clobbered by the bad multiplexer.

Detection of bad multiplexers was not a design goal of DesTestMAX, yet it seems like an entirely reasonable thing to try to add in a future version. Lee has shipped the bad-multiplexer in question so it may be used to verify the new test on real hardware.

Status: Open - see if it is possible to detect MUX errors before we rely on RAM.

Report 2

DesTestMAX detects error at address $0002

Michael reports that DesTestMAX detects a startup (blue border) error at address $0002 despite the fact that the C= 586220+ test reports no errors. Additionally, the C64 in question (250407 Rev C) boots to BASIC with 38911 bytes free and PEEKs and POKEs to address 2 work fine. The DesTestMAX cartridge in question works perfectly on two additional C64s (250469).

This is indeed mysterious. Location 2 is the first actual byte of RAM accessible and is the first to be tested (though the entire zero-page is tested before errors are reported). It is also odd that all 8 data bits show as bad.

The suggestion has been made to see what happens if the /RESET signal is brought low for a moment.

Status: Open - more investigation needed.

Issue Reports

Report 1

DesTestMAX halts with garbled screen

Report 2

DesTestMAX detects error at address $0002

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