Interrupt Controller
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
18-15
18.4.2
Baud-Rate Generators (BRGs)
The QUICC Engine subsystem contains four independent, identical baud-rate generators (BRGs)
that can be used with the UCCs. The clocks produced by the BRGs are sent to the bank-of-clocks
selection logic, where they can be routed to the controllers. Each BRG can be routed to one or
more UCCs. Figure 18-7 shows the block diagram for a BRG.
All BRGs can use BRGCLK as its source clock, or the external clock input selected by the value
of BRGCx[EXTC]. The BRGCLK is an internal signal generated in the clock synthesizer. The
external source option allows flexible baud-rate frequency generation, independent of the system
frequency. Additionally, the external source option allows a single external frequency to be the
source for more than one BRG. The external source signals are not synchronized internally
before being used by the BRG. The BRG provides a divide-by-16 option (BRGCx[DIV16]) and a
12-bit prescaler (BRGCx[CD]) to divide the source clock frequency. The combined source-clock
divide factor can be changed on-the-fly, except when changing to or from a CD value of 1, 2, or
3. For these values, disable the BRG and reset it before you program the new value. In addition,
you should not make two changes within two source clock periods. If the BRG divides the clock
by an even value, the transitions of BRGOn always occur on the rising edge of the source clock.
If the divide factor is odd, the transitions alternate between the falling and rising edges of the
source clock. The output of the BRG can be sent to the autobaud control block.
18.5
Interrupt Controller
The QUICC Engine subsystem interrupt controller sends general interrupts to the DSP cores in
the MSC8144E device. The core must then initiate the correct interrupt service routine to handle
the interrupt. Typically, this routine must read the interrupt status registers in the QUICC Engine
subsystem to determine the appropriate action to take. For some specific interrupts, the
MSC8144E uses five general configuration registers to expedite some interrupt responses:
Figure 18-7. Baud-Rate Generator (BRG) Block Diagram
Clock
Source
MUX
Divide by
1 or 16
Prescaler
12-Bit Counter
1–4,096
DIV 16
CD[5–8]
BRGOn Clock
BRGCLK
EXTC
Control
RXDn
To
Bank of Clocks
BRGn
Ext. Clock
Содержание MSC8144E
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