User’s Manual 9Table 2-1 provides estimates of the operating power for selected clock speeds.2.2.3 Time/Date OscillatorThe 32.768 kHz oscillator drives an external 32.768 kHz quartz crystal. The 32.768 kHzclock is used to drive a battery-backable (there is a separate power pin) internal 48-bitcounter that serves as a real-time clock (RTC). The counter can be set and read by soft-ware and is intended for keeping the date and time. There are enough bits to keep the datefor more than 100 years. The 32.768 kHz oscillator is also used to drive the watchdogtimer and to generate the baud clock for serial port A during the cold boot sequence.2.2.4 Parallel I/OThere are 40 parallel input/output lines divided among five 8-bit ports designated Athrough E. Most of the port lines have alternate functions, such as serial data or chip selectstrobes. Parallel ports D and E have the capability of timer-synchronized outputs. The out-put registers are cascaded.Figure 2-1. Cascaded Output Registers for Parallel Ports D and EStores to the port are loaded in the first-level register. That register in turn is transferred tothe output register on a selected timer signal. The timer signal can also cause an interruptthat can be used to set up the next bit to be output on the next timer pulse. This feature canbe used to generate precisely controlled pulses whose edges are positioned with high accu-racy in time. Applications include communications signaling, pulse width modulation anddriving stepper motors.Table 2-1. Operating Power Estimates at Selected Clock SpeedsClock Speed(MHz)Voltage(V)Current(mA)Power(mW)Clock Speed(MHz)Voltage(V)Current(mA)Power(mW)25.0 5.0 80 400 6.0 2.5 10 2512.5 5.0 40 200 3.0 2.5 5 1212.5 3.3 26 87 1.5 2.5 2.5 66.0 3.3 13 42 0.032 2.5 0.054 0.135Timer ClockLoad ClockLoad DataPort Output
