C509-L_97 Datasheet, PDF (168/290 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C509-L
6.5.2 Serial Interface 1
6.5.2.1 Operating Modes of Serial Interface 1
The serial interface 1 is an asynchronous unit only and is able to operate in two modes, as an 8-bit
or 9-bit UART. These modes, however, correspond to the above mentioned modes 1, 2 and 3 of
serial interface 0. The multiprocessor communication feature is identical with this feature in serial
interface 0. The serial interface 1 has its own interrupt request flags Rl1 and Tl1 which have a
dedicated interrupt vector location. The baud rate clock for this interface is generated by a
dedicated baud rate generator.
Mode A: 9-bit UART, variable baud rate:
11 bits are transmitted (through TXD1) or received (through RXD1): a start bit (0), 8 data bits (LSB
first), a programmable 9th bit, and a stop bit (1). On transmission, the 9th data bit (TB81 in S1CON)
can be assigned to the value of 0 or 1. For example, the parity bit (P in the PSW) could be moved
into TB81 or a second stop bit by setting TB81 to 1. On reception the 9th data bit goes into RB81
in special function register S0CON, while the stop bit is ignored. In fact, mode A of serial interface
1 is identical with mode 2 or 3 of serial interface 0 in all respects except the baud rate generation.
Mode B: 8-bit UART, variable baud rate:
10 bits are transmitted (through TXD1) or received (through RXD1): a start bit (0), 8 data bits (LSB
first), and a stop bit (1). On reception, the stop bit goes into RB81 in special function register
S1CON. In fact, mode B of serial interface 1 is identical with mode 1 of serial interface 0 in all
respects except for the baud rate generation.
In both modes, transmission is initiated by any instruction that uses S1BUF as a destination
register. Reception is initiated by the incoming start bit if REN1 = 1. The serial interfaces also
provide interrupt requests when a transmission or a reception of a frame has completed. The
corresponding interrupt request flags for serial interface 1 are Tl1 or Rl1, respectively. The interrupt
request flags Tl1 and Rl1 can also be used for polling the serial interface 1 if the serial interrupt shall
not be used (i.e. serial interrupt 1 not enabled).
The control and status bits of the serial channel 1 in special function register S1CON and the
transmit/receive data register S1BUF are shown on the next page. Writing to S1BUF loads the
transmit register and initiates transmission. Reading out S1BUF accesses a physically separate
receive register.
Note that these special function registers are not bit-addressable. Due to this fact bit instructions
cannot be used for manipulating these registers. This is important especially for S1CON where a
polling and resetting of the Rl1 or Tl1 request flag cannot be performed by JNB and CLR instructions
but must be done by a sequence of byte instructions, e.g.:
LOOP:
MOV
JNB
ANL
A,S1CON
ACC.0,LOOP
S1CON,#0FEH
;Testing of RI1
;Resetting of RI1
Semiconductor Group
6-90
1997-10-01