mcf5407 Freescale Semiconductor, Inc, mcf5407 Datasheet - Page 371

• Manufacturer Part Number: mcf5407
• Description: Mcf5407 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

14.5.2.2.1 AC ‘97 Low-Power Mode
A general-purpose I/O (GPIO) must be used as an AC ‘97 reset output pin. UART1
monitors the first three time slots of each Tx frame to detect the power-down condition for
the AC ‘97 digital interface. The power-down condition is detected as follows:
Low-power mode can be left through either a warm or cold reset. The CPU performs a
warm reset by setting MODCTL[AWR] for at least 1 µs. This negates RTS, which is used
as the frame sync output in AC ‘97 mode. The CPU performs a cold reset in two steps:
Step 2 is required so UART1 knows when an AC ‘97 cold reset is occurring.
14.5.2.3 Receiver
The receiver is enabled through its UCRn, as described in Section 14.3.10, “UART
Command Registers (UCRn).” Figure 14-34 shows receiver functional timing.
1. The first 3 bits of slot 1 must be set, indicating that the Tx frame and slots 1 and 2
2. Slot 2 holds the address of the power-down register (0x26) in the external AC ‘97
3. Slot 3 contains a 1 in the fourth bit (bit 12/PR4 in power-down register 1), as defined
1. Writes a 0 to whichever GPIO is being used as the active low AC ‘97 reset pin for
2. Writes a 0 to UART1’s MODCTL[ACRB] (bit 7). The CPU sets this bit after writing
are valid.
device.
in the AC ’97 specification.
the minimum time specified in the AC ‘97 specification.
a 1 to the GPIO used for the AC ‘97 reset pin.
Chapter 14. UART Modules
Operation
14-29