MC68HC11PH8 Datasheet, PDF (111/264 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

6
MOTOROLA INTERCONNECT BUS (MI BUS)
The Motorola Interconnect Bus (MI BUS) is a serial communications protocol which supports
distributed real-time control efficiently and with a high degree of noise immunity, at a typical bit rate
for the data transfer of 20kHz. The MI BUS is suitable for medium speed networks requiring very
low cost multiplex wiring; only one wire is required to connect to slave devices.^†
The MI BUS uses a push-pull sequence to transfer data. The master device, which in this case is
6
the MC68HC11PH8, sends a push field to the slave devices connected to the bus. The push field
contains data plus an address that is recognized by one of the slaves. The slave addressed returns
data which the master pulls from the MI BUS over the same wire. Specific details of the message
format are covered later in this section. The MCU (master) can take the bus at any time, with a
start bit that violates the rules of Manchester biphase encoding. Up to eight slave devices may be
addressed by the MI BUS. Other features of MI BUS include message validation, error detection,
and default value setting.
On the MC68HC11PH8 the MI BUS module shares the same pins on port G as the SCI2 module.
Data is transmitted (or ‘pushed’) via the TXD pin, and received (‘pulled’) via the RXD pin. While
data is being pushed, RXD will be disconnected from the receiver circuitry. The message frame is
handled automatically in hardware. The MCU register interface is similar to that for the SCI.
Pin
Alternate
function
PG0
RXD2
PG1
TXD2
MI BUS functions are enabled by MIE2 in S2CR1
† Related information on Motorola’s MI BUS is contained in the following Motorola publications:
EB409/D — The MI BUS and Product family for Multiplexing Systems
AN475/D — Single Wire MI BUS Controlling Stepper Motors
BR477/D — Smart Mover – Stepper Motors with Integrated Serial Bus Controller
MC68HC11PH8
MOTOROLA INTERCONNECT BUS (MI BUS)
TPG
MOTOROLA
6-1