Freescale Semiconductor MPC8260 - Manual (Page 632)

Baud-Rate Generators (BRGs)
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
17-2 Freescale Semiconductor
source for multiple BRGs. 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; however,
two changes should not occur within two source clock periods.
The prescaler output is sent internally to the bank of clocks and can also be output externally on BRGOn
through the parallel I/O ports. If the BRG divides the clock by an even value, the transitions of BRGOn
always occur on the falling edge of the source clock. If the divide factor is odd, the transitions alternate
between the falling and rising edges of the source clock. Additionally, the output of the BRG can be sent
to the autobaud control block.
17.1 BRG Configuration Registers 1–8 (BRGC x)
The BRG configuration registers (BRGCx) are shown in Figure 17-2 . A reset disables the BRG and drives
the BRGO output clock high. The BRGC can be written at any time with no need to disable the SCCs or
external devices that are connected to BRGO. Configuration changes occur at the end of the next BRG
clock cycle (no spikes occur on the BRGO output clock). BRGC can be changed on-the-fly; however, two
changes should not occur within a time equal to two source clock periods.
Table 17-1 describes the BRGCx fields.
0 13 14 15
Field — RST EN
Reset 0000_0000_0000_0000
R/W R/W
Addr 0x0x119F0 (BRGC1), 0x0x119F4 (BRGC2), 0x0x119F8 (BRGC3), 0x0x119FC (BRGC4),
0x0x115F0 (BRGC5), 0x0x115F4 (BRGC6), 0x0x1115F8 (BRGC7), 0x0x115FC (BRGC8)
16 17 18 19 30 31
Field EXTC ATB CD DIV16
Reset 0000_0000_0000_0000
R/W R/W
Addr 0x119F22 (BRGC1), 0x119F6 (BRGC2), 0x119FA (BRGC3), 0x119FE (BRGC4),
0x115F2 (BRGC5), 0x115F6 (BRGC6), 0x115FA (BRGC7), 0x115FE (BRGC8)
Figure 17-2. Baud-Rate Generator Configuration Registers (BRGC x)