Rainbow Electronics AT89C51SND1C - Manual (Page 159)

159
AT8xC51SND1C
4109E–8051–06/03
Figure 124. 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 125 through Figure 128.
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 125 through Figure 128, 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 136 through Table 128.
S
Slave Address
SCL
SDA
MSB
R/W
direction
ACK
signal
Nth data Byte ACK
signal
P/S
bit from
receiver
from
receiver
1 2 8 9 1 2 8 9
Clock Line Held Low While Serial Interrupts Are Serviced