Datasheet

128
AT89C5132
4173C–USB–07/04
Figure 105. Complete Data Transfer on TWI Bus
The four operating modes are:
• Master transmitter
• Master receiver
• Slave transmitter
•Slave receiver
Data transfer in each mode of operation are shown in Figure 106 through Figure 109.
These figures contain the following abbreviations:
A Acknowledge bit (low level at SDA)
A
Not acknowledge bit (high level on SDA)
Data 8-bit data Byte
S START condition
P STOP condition
MR Master Receive
MT Master Transmit
SLA Slave Address
GCA General Call Address (00h)
R Read bit (high level at SDA)
W Write bit (low level at SDA)
In Figure 106 through Figure 109, circles are used to indicate when the serial interrupt
flag is set. The numbers in the circles show the status code held in SSSTA. At these
points, a service routine must be executed to continue or complete the serial transfer.
These service routines are not critical since the serial transfer is suspended until the
serial interrupt flag is cleared by software.
When the serial interrupt routine is entered, the status code in SSSTA is used to branch
to the appropriate service routine. For each status code, the required software action
and details of the following serial transfer are given in Table 20 through Table 109.
S
Slave Address
SCL
SDA
MSB
R/W
direction
ACK
signal
Nth data Byte ACK
signal
P/S
bit from
receiver
from
receiver
12 89 12 89
Clock Line Held Low While Serial Interrupts Are Serviced