| SDC68k_2 [message #9459] |
Wed, 08 December 2021 03:49  |
gbm
Messages: 34
Registered: January 2018
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New kid on the block, a continuation of my SDC saga with a little mystery.
This is the smallest (so far) computer based on a classic microprocessor, this time with a MC68SEC000. Like the previous SDC models, it has a button, 4 LEDs, terminal interface via USB CDC and a mass storage (16 MiB) for emulating diskettes, so it's capable of running CP/M-68k or alike. RAM capacity is 512 KiB. Size approx. 1 x 1.5" or 2.5 x 4 cm. As with SDC68k, the real operational speed is equivalent to 1.7 MHz with no wait states. Vectored interrupt controller is implemented for demonstrating the capabilities of 68k interrupt system - I use the SDC computers for demonstrating various aspects of computer operation to students.
And now the little mystery: according to Motorola/Freescale/NXP docs, the 68EC000 and SEC000 models, unlike 68000 and like 68010, support MOVE from CCR and prohibit MOVE from SR in User mode. The hardware monitor shows something different - the CPU doesn't signal illegal operation on MOVE from SR in User mode and MOVE from CCR is undefined. Is this an error in the docs or my CPU is not the proper 68SEC000 (then what model it could be in this package? . Any ideas/explanations? The CPU is from ebay/China, so it could be fake but then it is still not clear what would it be "converted" (remarked) from. It is clearly low power CMOS.
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