Introduction
1-6
MC68307 USER’S MANUAL
MOTOROLA
1.2.2.5 INTERRUPT CONTROLLER. The SIM07 coordinates all interrupt sources, both
from on-chip peripherals (timer1, timer2, M-bus, and UART) and off-chip inputs (IRQ7, and
INT1–INT8). It provides interrupt requests to the EC000 core with programmable priority
level, and responds to acknowledge cycles by providing programmed vectors unique to
each source.
1.2.3 Timer Module
The timer module comprises two independent, identical general-purpose timers, and a soft-
ware watchdog timer. Each general-purpose timer block contains a free-running 16-bit timer
that can be used in various modes, to capture the timer value with an external event, to trig-
ger an external event or interrupt when the timer reaches a set value, or to count external
events. Each has an 8-bit prescaler to allow a programmable clock input frequency derived
from the system clock or external count input. The output pins (one per timer) have a pro-
grammable mode.
A software watchdog timer is also provided for system protection. If required, this resets the
EC000 core if it is not refreshed periodically by software.
1.2.4 UART Module
The MC68307 contains a full-duplex UART module, with an on-chip baud-generator provid-
ing both standard and nonstandard baud rates up to 5 Mb/s. The module is functionally
equivalent to the MC68681 DUART, although only one serial channel is implemented. Data
formats can be 5, 6, 7, or 8 bits with even, odd, or no parity and up to two stop bits 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.
Clocking is provided by the MC68307 system clock, via a programmable prescaler allowing
various baud rates to be chosen. Modem support is provided with request-to-send (RTS)
and clear-to-send (CTS) lines available. The serial port can sustain data rates of 5 Mbps.
1.2.5 M-Bus Module
The M-bus interface module provides a two-wire, bidirectional serial bus which provides a
simple, efficient way for data exchange between devices. It is compatible with the I2C-bus
standard. M-bus minimizes the interconnection between devices in the end-system. It is
best suited for applications which need occasional bursts of fast communication over a short
distance, among a number of devices. The maximum data rate is limited to 595 kbps at
16.67 MHz (100 kbps to be compatible with I2C), the maximum communication length and
number of devices which can be connected are limited physically by the maximum bus
capacitance and logically by the number of unique addresses.
The M-bus system is a true multimaster bus including collision detection and arbitration to
prevent data corruption if two or more masters intend to control the bus simultaneously. This
feature provides the capability for complex applications with multiprocessor control. It may
also be used for rapid testing and alignment of end products via external diagnostic connec-
tions.