SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 60

• Manufacturer Part Number: SAB80C517-M16
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

7.2.2
7.2.2.1 Operating Modes of Serial Interface 1
The serial interface 1 is an asynchronous channel 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 (see section 8 for more details about the interrupts). The baud
rate clock for this interface is generated by a dedicated baud rate generator. A more detailed
description how to set the baud rate follows in section 7.2.2.3 and 7.2.2.4.
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
(see section 7.2.2.3).
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 (see section 7.2.2.3).
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, resp. See section 8 for
more details about the interrupt structure. 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 are illustrated
in figure 7-12. Figure 7-13 shows the special function register S1BUF which is the data register for
receive and transmit. 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:
Semiconductor Group
Serial Interface 1
MOV
JNB
ANL
A,S1CON
ACC.0,LOOP
S1CON,#0FEH ;Resetting of RI1
;Testing of RI1
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On-Chip Peripheral Components