EZ80F91MCU Datasheet, PDF (53/396 Pages) Zilog, Inc. – eZ80Acclaim-TM Flash Microcontrollers

eZ80F91 MCU
Product Specification
34
50 Mhz while the X_OUT pin is unconnected. In the other mode, the X_IN and X_OUT
pins can be driven by a crystal circuit.
Crystals recommended by ZiLOG are defined to be a 50 Mhz–3 overtone circuit or
1–10 MHz range fundamental for PLL operation. For details, refer to the On-Chip
Oscillators section on page 342.
Real Time Clock. An internal 32 KHz real-time clock crystal oscillator driven by
either the on-chip 32768 Hz crystal oscillator or a 50/60 Hz power-line frequency
input. While intended for timekeeping, the RTC 32 KHz oscillator can be selected
as an SCLK. RTC_V_DD and RTC_V_SS provide an isolated power supply to ensure
RTC operation in the event of loss of line power when a battery is provided. For
details, refer to the On-Chip Oscillators section on page 342.
PLL Clock. The eZ80F91 internal PLL driven by external crystals or can oscillators
in the 1 MHz to 10 MHz range to generate an SCLK up to 50 MHz. For details, refer
to the Phase-Locked Loop section on page 320.
SCLK Source Selection Example
If an application must run the eZ80F91 device at 40 MHz, the following solutions
are possible:
• Use a 40MHz–3rd overtone crystal (not recommended due to its weak funda-
mental rating)
• Use a 40MHz can oscillator (expensive)
• Use an 8MHz fundamental two-pin crystal and program the internal PLL with
a multiplier of five to achieve 40 MHz (inexpensive).
PS019209-0504
PRELIMINARY
Architectural Overview