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C165UTAH
Asynchronous/Synchr. Serial Interface
Data Sheet
264
2001-02-23
S0TBIC
SFR
Reset Value: - - 00
H
3
2
Note:
Please refer to the general Interrupt Control Register description on page 109 for
an explanation of the control fields.
12.1.4
General Operation
The ASC supports full-duplex asynchronous communication up to 2.25 MBaud and half-
duplex synchronous communication up to 4.5 MBaud (@ 36 MHz CPU clock which is
equal to the ASC module clock). In synchronous mode, data are transmitted or received
synchronous to a shift clock which is generated by the microcontroller. In asynchronous
mode, 8- or 9-bit data transfer, parity generation, and the number of stop bits can be
selected. Parity, framing, and overrun error detection is provided to increase the
reliability of data transfers. Transmission and reception of data is double-buffered. For
multiprocessor communication, a mechanism to distinguish address from data bytes is
included. Testing is supported by a loop-back option. A 13-bit baudrate timer with a
versatile input clock divider circuitry provides the ASC with the serial clock signal. In a
special asynchronous mode, the ASC supports IrDA data transmission up to 115.2
kBaud with fixed or programmable IrDA pulse width. A autobaud detection unit allows to
detect asynchronous data frames with its baudrate and mode with automatic initialization
of the baudrate generator and the mode controll bits.
A transmission is started by writing to the Transmit Buffer register S0TBUF. Only the
number of data bits which is determined by the selected operating mode will actually be
transmitted, ie. bits written to positions 9 through 15 of register S0TBUF are always
insignificant.
Data transmission is double-buffered, so a new character may be written to the transmit
buffer register, before the transmission of the previous character is complete. This allows
the transmission of characters back-to-back without gaps.
Data reception is enabled by the Receiver Enable Bit CON_REN. After reception of a
character has been completed, the received data and, if provided by the selected
operating mode, the received parity bit can be read from the (read-only) Receive Buffer
register S0RBUF. Bits in the upper half of S0RBUF which are not valid in the selected
operating mode will be read as zeros.
Data reception is double-buffered, so that reception of a second character may already
begin before the previously received character has been read out of the receive buffer
register. In all modes, receive buffer overrun error detection can be selected through bit
S0
EIR
S0
EIE
5
4
1
0
11
10
9
8
7
6
15
14
13
12
rw
rw
-
-
-
-
rw
rw
-
-
-
-
GLVL
ILVL