SERIAL COMMUNICATION INTERFACE (SCI)
6 - 24
PORT C
MOTOROLA
and the 8-bit synchronous mode, the PE bit is always cleared since there is no parity bit
in these modes. If the byte received causes both parity and overrun errors, the SCI receiv-
er will only recognize the overrun error.
6.3.2.2.7
SSR Framing Error Flag (FE) Bit 6
The FE bit is set in the asynchronous modes when no stop bit is detected in the data string
received. FE and RDRE are set simultaneously – i.e., when the received word is trans-
ferred to the SRX. However, the FE flag inhibits further transfer of data into the SRX until
it is cleared. FE is cleared when the SCI status register is read followed by reading the
SRX. The hardware, software, SCI individual, and stop reset also clear FE. In the 8-bit
synchronous mode, FE is always cleared. If the byte received causes both framing and
overrun errors, the SCI receiver will only recognize the overrun error.
6.3.2.2.8
SSR Received Bit 8 Address (R8) Bit 7
In the 11-bit asynchronous multidrop mode, the R8 bit is used to indicate whether the re-
ceived byte is an address or data. R8 is not affected by reading the SRX or status register.
The hardware, software, SCI individual, and stop reset clear R8.
6.3.2.3
SCI Clock Control Register (SCCR)
The SCCR is a 16-bit read/write register which controls the selection of the clock modes
and baud rates for the transmit and receive sections of the SCI interface. The control bits
are described in the following paragraphs. The SCCR is cleared by hardware reset.
The basic points of the clock generator are as follows:
1.
The SCI core always uses a 16
×
internal clock in the asynchronous modes
and always uses a 2
×
internal clock in the synchronous mode. The maximum
internal clock available to the SCI peripheral block is the oscillator frequency
divided by 4. With a 40-MHz crystal, this gives a maximum data rate of 625
Kbps for asynchonous data and 5 Mbps for synchronous data. These maxi-
mum rates are the same for internally or externally supplied clocks.
2.
The 16
×
clock is necessary for the asynchronous modes to synchronize the
SCI to the incoming data (see Figure 6-11).
3.
For the asynchronous modes, the user must provide a 16
×
clock if he wishes
to use an external baud rate generator (i.e., SCLK input).
4.
For the asynchronous modes, the user may select either 1
×
or 16
×
for the
output clock when using internal TX and RX clocks (TCM=0 and RCM=0).
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
.
..
Содержание DSP56002
Страница 380: ......
Страница 382: ......
Страница 390: ...Freescale Semiconductor I Freescale Semiconductor Inc For More Information On This Product Go to www freescale com nc...