User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 10: Serial Interfaces Page
351
L
INE
I
NTERFACE
C
ONFIGURATION
The line interface is configured in the
ser_mode
and
ser_line_mode
registers. On reset the clock source
defaults to use the internal baud rate clock, ensuring that state is correctly cleared. Since changes to the line
mode register can change the clocking of the interface block care must be taken when it is written: all previous
configuration requests must have completed before the
ser_line_mode
register is written, and no additional
registers should be written until the
ser_line_mode
register write has completed. Any requests that are in
progress close in time to when the
ser_line_mode
register is written will have UNPREDICTABLE results. The
recommended way to safely change the
ser_line_mode
register is to first read the
ser_mode
register and use
the result (or use a SYNC) then write the
ser_line_mode
register and read it back and again use the result.
S
YNCHRONOUS
S
ERIAL
I
NTERRUPTS
The DMA interrupts for each channel are combined with status interrupts, and made available in the
ser_status
register. Bits in this register are masked by the
ser_int_mask
register and combined to generate
the system interrupts 10 (for channel 0) and 11 (for channel 1). Reading the
ser_status
register will clear all
bits in it. For a description of DMA interrupts associated with the serial channels, please refer to
.
To allow debuggers non-intrusive access to the status register, it is also made available through the
ser_status_debug
register, which does not clear the status on read.
S
YNCHRONOUS
S
ERIAL
L
OOPBACK
There are two loopback configurations in the synchronous serial port. In both cases the transmitter output is
connected internally to the receiver input. The first configuration relies on external timing pulses and uses TIN
and RIN as normal. The second configuration has TIN always active and internally connects RIN to the
RTST_STROBE output. These are shown in
. When the second loopback mode is used the line
interface configuration for both tx and rx can be set to the values in
to allow a table
driven loopback.
Figure 73: Synchronous Serial Loopback Connections
enable
data_out
loopback_enable
data_in
1
0
tout
loopback_enable
rin
1
0
loopback_strobe_mode
T
OUT
R
IN
D
OUT
D
IN
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