xx21 series hardware features

[gut@xxxxxxxxxxxxxxxxx (alex lasky)]

Apologies if the following topics have been covered before, but I'm new
to the list.

Part 1

I was (favourably) amazed by the F21 (& MuP21) when I first read the
summary of features in the microcontroller FAQ. Its combination of 200
MIPS speed, onboard video and analog processors, very low power
consumption and low (predicted) cost seemed very compelling. But on closer
inspection of the details my pulse slowed. It seems the chip was developed
with a number of different applications in mind at different stages.

First of all, what is the use of an NTSC video output providing Commodore64
style graphics in only 16 colours to a TV? If the chip is to be used in a
low-cost mass-market multimedia device intended for connection to a TV, you
would need more than 16 colours; this is 1996 after all, and Commodore is no
longer with us (in the USA at least). While 16 colour graphics is cheap, it
is only really suitable for CAD and office applications (word processing,
databases, spreadsheets and the like). Yet the low resolution and the
inappropriateness of TV's in these applications rules it out.

The F21's promised RGB superVGA output is a step in the right direction,
but having the signal encoded onto a single pin would then require additional
external circuitry, which defeats the purpose somewhat. In addition, some of
the vaunted applications such as PDA's and embedded controllers would use
LCD displays rather than CRT's (if any), making the circuitry redundant for many of the
perceived applications. Also what is the nature of the "digital data encoded
onto the video signal". Teletext? Although having on-chip video generation
is remarkable and desirable, the extra real estate, design and power
consumption required to produce a USEFUL signal may rule it out as a
desirable feature when coupled with the lack of flexibility produced.

Similar considerations apply with the analog processor. Once again, wonderful
for a multimedia machine on a chip, but at 6 bits it is more than a little
rough, especially for audio, which seems to be the whole point. Oversampling
can only go so far! Once again, producing a USEFUL signal detracts from the
low cost and minimalist ethos of the chip.

End of Part 1 (to be continued)



Alex Lasky            * "Clubland & dubland will bop till they drop, then
gut@elec.apana.org.au * discuss postmodernism & the punk ethos over pools of
Sydney, Australia     * 70%-proof vomit on the toilet floor" - Ian Mcdonald