mc68hc05bs8 Freescale Semiconductor, Inc, mc68hc05bs8 Datasheet - Page 74

• Manufacturer Part Number: mc68hc05bs8
• Description: Mc68hc05 Family Of Low-cost Single-chip Microcontrollers.
• Manufacturer: Freescale Semiconductor, Inc

8
is accomplished with MAL=1 and MSTA=0. If one master attempts to start transmission while the
bus is being controlled by another master, the transmission will be inhibited; the MSTA bit will be
changed from 1 to 0 without generating STOP condition; an interrupt will be generated and the
MAL bit set to indicate that the attempt to acquire the bus has failed. Considering these cases, the
slave service routine should test the MAL bit first, and software should clear the MAL bit if it is set.
8.5
Port pins PC6 and PC7 are designed with a hardware interrupt circuit for the software supported
M-Bus interface to detect the “Start” condition of the M-Bus protocol. This interrupt uses the same
interrupt vector as for the hardware M-Bus interrupts, at address $3FF2 and $3FF3. The user is
responsible for determining the source of the M-Bus interrupt in the interrupt service routine by
reading the flags.
8-14
PC7/SDA2
PC6/SCL2
PC7/SDA2
PC6/SCL2
SIIC
INT
Software Supported M-Bus Interface
Figure 8-5 Software Supported M-Bus Interrupt
START
&
M-BUS SERIAL INTERFACE
D
C
R
Q
INT interrupt request
Reset or SIFC
STOP
MC68HC05BS8
TPG