MC68HC11PH8 Datasheet, PDF (112/264 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

6.1
Push-pull sequence
Communication between the MCU and the slave device always utilizes the same frame
organization. First, the MCU sends serial data to the selected device. This data field is called the
‘push field’. At the end of the push field, the selected device automatically sends back to the MCU
the data held during the push sequence. The MCU reads the serial data sent by the selected
device. This data is called the ‘pull field’ and contains status information followed by the
end-of-frame information from the selected device.
Time slots
Push-pull function
Push (biphase coded)
Pull (NRZ coded)
6
TXD pin (true data)
10
01
MI BUS wire
01234567
Start
Stop
Bit Þelds
Start
Push
sync
D0
D1
D2
D3
D4
A0
A1
A2
Pull
sync
Data
Address
Push Þeld
(driven by MCU)
Message frame
NRZ
Data
End of frame
Pull Þeld
(driven by slave)
Figure 6-1 MI BUS timing
6.1.1 The push field
The push field consists of a start bit, a push synchronization bit, a push data field and a push
address field. The start consists of three time slots having the dominant logical state ‘0’. The start
marks the beginning of the message frame by violation of the rule of the Manchester code. The
push synchronization bit consists of a biphase coded ‘0’. Biphase coding will be discussed later.
The push data field consists of five bits of biphase coded data. The push address consists of three
bits of biphase coded data. Data and address are written to the lower byte of the SCI data register
(S2DRL). The push data occupies the lower five bits and the push address occupies the upper
three bits of the register.
MOTOROLA
6-2
MOTOROLA INTERCONNECT BUS (MI BUS)
TPG
MC68HC11PH8