pc87591l-n05 National Semiconductor Corporation, pc87591l-n05 Datasheet - Page 196

• Manufacturer Part Number: pc87591l-n05
• Description: Lpc Mobile Embedded Controller
• Manufacturer: National Semiconductor Corporation

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4.0 Embedded Controller Modules
4.13.9 Usage Hints
1. When the ACB is disabled, BB in ACBnCST register is cleared. After the ACB is enabled (by setting ENABLE in
2. When waking up from power-down before checking MATCH in ACBnCST register, check BUSY in the same register to
3. The BB bit can help solve a deadlock in which two or more devices detect a usage conflict on the bus and both cease
4. In some cases, the bus may get stuck with the SCL and/or SDA lines active, such as when an erroneous Start or Stop
ACBnCTL2 register), the bus may be in the middle of a transaction with another device in systems with more than one
master. This status is not reflected by BB.
To prevent bus errors, the ACB must synchronize with the bus activity status before issuing a request to become the bus
master for the first time. The software should check that there is no activity on the bus by checking the BB bit after the
time-out period allowed by the bus.
make sure that the address transaction is completed.
being bus masters at the same time. In this situation, the BB bits of both devices are active (because each “detects”
another master currently performing a transaction, while in fact there is no transaction). This potentially causes the bus
to stay locked until a device on the bus sends a Stop Condition (through STOP in ACBnCTL1 register).
The BB bit allows the software to monitor bus usage so that it can detect whether the bus remains unused over a certain
period of time while BB is set. It also avoids sending a STOP signal in the middle of the transaction of another device on
the bus.
Condition occurs in the middle of a slave receive session.
If the SCL line is stuck active, the module that holds the bus must release it.
If the SDA line is stuck active, the sequence below releases the bus (Note: In normal cases, SCL may be toggled only
by the bus master; this sequence is a recovery scheme which is an exception and should be only used if there is no other
master on the bus):
a. Disable and re-enable the module to set it for the Slave mode not addressed.
b. Set START in ACBnCTL1 register to attempt to issue a Start Condition.
c. Check if the SDA line is active (low) by reading TSDA in ACBnCST register. If it is active, issue a single SCL cycle
d. Check if MASTER in ACBnST register is set, which indicates that the Start Condition was sent. If it is not set, repeat
e. Clear BB. This enables START to be executed. Continue according to “Bus Idle Error Recovery” on page 188.
by writing 1 to TGSCL in the same register. If it is not active, skip to step e.
step c and this step until the SDA is released.
(Continued)
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