AMD Geode SC2200 - Manual (Page 122)

128 AMD Geode™ SC2200 Processor Data Book
SuperI/O Module 32580B
5.7.3 Acknowledge (ACK) Cycle
The ACK cycle consists of two signals: the ACK clock pulse
sent by the master with each byte transferred, and the ACK
signal sent by the receiving device (see Figure 5-15).
The master generates the ACK clock pulse on the ninth
clock pulse of the byte transfer. The transmitter releases
the ABD line (permits it to go high) to allow the receiver to
send the ACK signal. The receiver must pull down the ABD
line during the ACK clock pulse, signalling that it has cor-
rectly received the last data byte and is ready to receive the
next byte. Figure 5-16 illustrates the ACK cycle.
Figure 5-15. ACCESS.bus Data Transaction
Figure 5-16. ACCESS.bus Acknowledge Cycle
S P
Start
Condition Stop
Condition
ABD
ABC
MSB
ACK ACK
1 2 3 - 6 7 8 9 1 2 3 - 8 9
Acknowledge
Signal From Receiver
Byte Complete
Interrupt Within
Receiver
Clock Line Held
Low by Receiver
While Interrupt
is Serviced
S
Start
Condition
ABC
1 2 3 - 6 7 8 9
Transmitter Stays Off Bus
During Acknowledge Clock
Acknowledge
Signal From Receiver
Data Output
by Transmitter
Data Output
by Receiver