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
341
shows an active high sync pulse. If the delay is 0, map entry 0 determines whether
data bit 0 is accepted or rejected. If that entry spans a single bit time, map entry 1 controls the disposition of
bit 1. Alternatively if the delay is configured as one and entry 0 spans 14 byte times, it determines the treatment
of bits 1 through 112.
Figure 69: Example Reception Using RIN as Active High Sync (sampling on the falling clock edge)
O
UTPUT
L
INE
I
NTERFACE
In the transmit direction, data is driven on pin DOUT either by an external clock signal, supplied on the
CTS_TCLKIN pin, or by the internal baud rate generator. The internal clock can be made available externally
on the COUT pin if enabled by setting bit 1 (channel 0) or bit 3 (channel 1) in the UART output port configuration
register (
duart_opcr
). The polarity of the transitioning clock edge is programmable. The DOUT pin will be high
impedance while the interface is disabled, so a pull-up may be required.
The output bits are optionally gated by means similar to the input:
1
Gapped Clock
: If the external device is supplying the clock on CTS_TCLKIN, it can omit clock pulses. Since
the BCM1250 never receives a clock pulse this method can always be used to suppress the transmission of
bits.
2
External Enable
: Regardless of clock source, the TIN pin can be supplied with an externally generated enable
signal. This is latched on the active edge of the clock and disables output 0, 1, 2 or 3 clocks later. The DOUT
pin is high impedance (undriven) when disabled.
3
Internal Sequencer
: Regardless of clock source, but exclusive with (2), the enable signal can be generated
by an internal sequencer, which is itself synchronized to the data stream by an edge or level on TIN. The
sequencer can also provide a strobe on the TSTROBE output.
The bit stream from the protocol engine is output on the DOUT pin on every enabled clock edge. During cycles
where the output is disabled DOUT is tri-stated following the clock edge and will be driven again following an
enabled clock edge.
Output Using an External Enable
The external enable on the TIN pin can be configured to be active high or low. The signal is delayed by 0 to 3
clock edges. If the delay is zero then the output is immediately enabled and will drive the current output data,
provided the enable signal is still asserted on the next active edge of the clock the data will change and new
data will be output. If the delay is nonzero the enable is sampled on the same edge of the clock that is used to
drive DOUT. TIN must be stable for at least a set-up time prior to that clock edge (in the usual case it will
transition on the opposite edge). When output is disabled, DOUT is tri-stated, and the bit stream supplied by
the protocol engine does not advance.
Clock
Time:
DIN
RIN/Sync
0
1
2
3