User’s Manual
3
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The built-in main clock oscillator uses an external crystal or more usually a ceramic
resonator. Typical resonator frequencies are in the range of 1.8 MHz to 29.5 MHz.
Since precision timing is available from the separate 32.768 kHz oscillator, a low-cost
ceramic resonator with ½ percent error is generally satisfactory. The clock can be dou-
bled or divided by 8 to modify speed and power dynamically. The I/O clock, which
clocks the serial ports, is divided separately so as not to affect baud rates and timers
when the processor clock is divided or multiplied. For ultra low power operation, the
processor clock can be driven from the separate 32.768 kHz oscillator and the main
oscillator can be powered down. This allows the processor to operate at approximately
100 µA and still execute instructions at the rate of approximately 10,000 instructions
per second. This is a powerful alternative to sleep modes of operation used by other
processors. The current is approximately 65 mA at 25 MHz and 5 V. The current is pro-
portional to voltage and clock speed—at 3.3 V and 7.68 MHz the current would be 13
mA, and at 1 MHz the current is reduced to less than 2 mA. Flash memory with auto-
matic power down (from AMD) should be used for operation at the lowest power.
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The excellent floating-point performance is due to a tightly coded library and powerful
processing capability. For example, a 25 MHz clock takes 14 µs for a floating add,
13 µs for a multiply, and 40 µs for a square root. In comparison, a 386EX processor
running with an 8-bit bus at 25 MHz and using Borland C is about 10 times slower.
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There is a built-in watchdog timer.
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The standard 10-pin programming port eliminates the need for in-circuit emulators. A
very simple 10 pin connector can be used to download and debug software using
Z-World’s Dynamic C and a simple connection to a PC serial port. The incremental cost
of the programming port is extremely small.
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