Freescale Semiconductor, Inc.
Each communication channel is completely independent. Data formats can be 5, 6, 7, or 8
bits with even, odd, or no parity and stop bits up to 2 in 1/16 increments. Four-byte receive
buffers and two-byte transmit buffers minimize CPU service calls. A wide variety of error
detection and maskable interrupt capability is provided on each channel. Full-duplex,
autoecho loopback, local loopback, and remote loopback modes can be selected.
Multidrop applications are supported.
A 3.6864-MHz crystal drives the baud rate generators. Each transmit and receive channel
can be programmed for a different baud rate, or an external 1× and 16× clock input can be
selected. Full modem support is provided with separate request-to-send (RTS) and clear-
to-send (CTS) signals for each channel. One channel also provides service request
signals. The two serial ports can sustain rates of 9.8 Mbps with a 25-MHz system clock in
1× mode, 612 kbps in 16× mode (6.5 Mbps and 410 kbps @ 16.78 MHz).
1.3.4 Timer Modules
Timers and counters are used in a system to monitor elapsed time, generate waveforms,
measure signals, keep time-of-day clocks, initiate DRAM refresh cycles, count events, and
provide “time slices” to ensure that no task dominates the activity of the processor. A
counter that counts clock pulses makes a timer, which is most useful when it causes
certain actions to occur in response to reaching desired counts.
The MC68340 has two, identical, versatile, on-chip counter/timers as well as a simple
timer in the SIM40. These general-purpose counter/timers can be used for precisely timed
events without the errors to which software-based counters and timers are susceptible—
e.g., errors caused by dynamic memory refreshing, DMA cycle steals, and interrupt
servicing. The programmable timer operating modes are input capture, output compare,
square-wave generation, variable duty-cycle square-wave generation, variable-width
single-shot pulse generation, event counting, period measurement, and pulse-width
measurement.
Each timer consists of a 16-bit countdown counter with an 8-bit countdown prescaler for a
composite 24-bit resolution. The two timers can be externally cascaded for a maximum
count width of 48 bits. The counter/timer can be clocked by the internal system clock
generated by the SIM40 (÷2) or by an external clock input. Either the processor or external
stimuli can trigger the starting and stopping of the counter. When a counter reaches a
predetermined value, either an external output signal can be driven, or an interrupt can be
made to the CPU32. The finest resolution of the timer is 80 ns with a 25-MHz system
clock (125 ns @ 16.78 MHz).
1.4 POWER CONSUMPTION MANAGEMENT
The MC68340 is very power efficient due to its advanced 0.8-µ HCMOS process
technology and its static logic design. The resulting power consumption is typically
900 mW in full operation @ 25 MHz (650 mW@ 16.78 MHz)—far less than the
comparable discrete component implementation the MC68340 can replace. For
applications employing reduced voltage operation, selection of the MC68340V, which
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MC68340 USER’S MANUAL
MOTOROLA
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