Telefunken RT200 User Information page 9

30 CLOCKIN
SEGMENT OUT
31
0
SEGMENT OUT
32
1
SEGMENT OUT
33
2
SEGMENT OUT
34
3
SEGMENT OUT
35
4
SEGMENT OUT
36
5
SEGMENT OUT
37
6
SEGMENT OUT
38
7
39 Vdd
40 CPU CLOCKIN Input
Luckily, these are all only digital functions and the processors works with a standard 5V supply and TTL
levels, which simplifies the selection for a new processor:
Selecting a Microprocessor Platform
The microcontroller market offers lots of different families and variants of controllers. Some of them are
well-known and for general-purpose use, some of them were designed with a specific application in mind.
Since the synthesizer's PLL loop (see below) is completely done in the PLL chip, the main CPU's
functionality mainly consists of driving the multiplexed display, querying the keys, running the internal
clock for the timer and moving around some data - all not very advanced tasks even a 4-bit CPU could
handle (I guess the original MN4500 is a 4-bit CPU!), but most 4-bit-CPUs are not general purpose and
difficult to get or require expensive development systems, so let's settle with an 8-bit core. What other
things do we need?
Must be available in CMOS, to allow operation from the built-in accumulator for power failures or
for times when the tuner is not connected to a mains supply.
Must be able to run with the slow 562.5kHz clock supplied by the synthesizer chip. Of course we
could add an own oscillator, but I already said that there is no need for much compute power and
the low clock helps keeping the power consumption low.
Must be available without problems. Not yet another obscure chip ;-)
Development tools must be available for free at best...
Summing up, I settled with a CPU family that is the most widely used family of 8-bit controllers: The 8051
family. Originally introduced by Intel, 8051 derivatives are available from more than a dozen of
manufacturers. The two 'standard' ROMless components 8031 and 8032 are available from probably more
than 10 different manufacturers. I finally settled for the 80C32, the variant with more internal RAM
(needed for the stations' frequency storage) and a third timer (not needed here). By coincidence, I got an
TS80C32X2 from Temic, formerly Telefunken Microelectronics. It has the nice capability of running in X2
mode, i.e. an internal frequency divider is turned off and the device runs at double speed with the same
external clock. A very nice feature, especially considering the low external clock frequency.
The other stuff around the CPU is pretty basic: an address latch to demultiplex address and data lines, an
EPROM for the code (the C32's internal RAM of 256 bytes is sufficient for this task), and some latches and
Input 250Hz clock from the syntesizer chip for the internal timer
Output segment data for the display + addr/data for the synthesizer chip
Output
Output
Output
Output
Output
Output
Output
---- 5V supply voltage
CPU clock input (562.5kHz)
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