BCM1250/BCM1125/BCM1125H
User Manual
10/21/02
B r o a d c o m C o r p o r a t i o n
Page
320
Section 10: Serial Interfaces
Document
1250_1125-UM100CB-R
S e c t i o n 1 0 : S e r i a l I n t e r f a c e s
I
NTRODUCTION
The part incorporates two identical serial ports that provide full-duplex interfaces to a variety of serial devices.
Each port is separately configured, and can be run as an asynchronous serial link from 1200 baud to 5 Mbaud
or a synchronous serial link at up to 55 Mbps.
In asynchronous mode the programming model is based on a DUART. Some registers share information
between the A and B channels, but the two ports can be independently switched to the synchronous mode.
In synchronous mode the serial interface includes an internal HDLC engine and externally provides a PCM
highway style link.
Selection between asynchronous and synchronous interfaces is normally made at reset time using the
configuration input on IO_AD[12] (channel A) and IO_AD[14] (channel B). However, the CPU can write the
corresponding bits in the
system_cfg
register to change the selection. Modifying this bit will switch the output
pins between the asynchronous drivers and the synchronous ones. If the interface is switched between modes
software will need to re-initialize the interface and may need to reset the external device.
Each serial port has 8 pins associated with it. In addition if an interface is in synchronous mode it can use one
of the GPIO pins as an output (software cannot change the use of this pin, it can only be set by the reset
configuration). The following table shows their use in each mode, and for asynchronous mode the
correspondence between the pins and input or output registers for channel A and channel B.
Table 195: Serial Interface Signal Names
Pin Name
Direction A
B
Asynchronous Mode
Synchronous Mode
DOUT
Output
Transmit data output
Transmit data output
DIN
Input
Receive data input
Receive data input
RTS_
TSTROBE
Output
op[0]
op[1]
RTS output or general output
Transmit strobe output
COUT
Output
op[2]
op[3]
General output (e.g. for DTR handshake) or baud
rate clock output
Clock output
CTS_
TCLKIN
Input
ip[0]
ip[1]
CTS input, or general input with transision detector Transmit clock input
CIN_
RCLKIN
Input
ip[2]
ip[3]
General input with transition detector (e.g. for DSR
handshake)
Receive clock input
TIN
Input
ip[4]
ip[5]
General input (e.g. for DCD)
Transmit enable or
synchronization input
RIN
Input
ip[6]
ip[7]
General input (e.g. for RI)
Receive enable or
synchronization input
RSTROBE
(shared
with GPIO)
Output
Receive strobe output
(if this is not enabled the
pins are used for GPIO[0]
or GPIO[1])
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