Philips Semiconductors Product specification
80C51/87C51/80C52/87C52
80C51 8-bit microcontroller family
4 K/8 K OTP/ROM low voltage (2.7 V–5.5 V),
low power, high speed (33 MHz), 128/256 B RAM
2000 Aug 07
16
and 1 and exclude Slave 2 use address 1110 0100, since it is
necessary to make bit 2 = 1 to exclude slave 2.
The Broadcast Address for each slave is created by taking the
logical OR of SADDR and SADEN. Zeros in this result are trended
as don’t-cares. In most cases, interpreting the don’t-cares as ones,
the broadcast address will be FF hexadecimal.
Upon reset SADDR (SFR address 0A9H) and SADEN (SFR
address 0B9H) are leaded with 0s. This produces a given address
of all “don’t cares” as well as a Broadcast address of all “don’t
cares”. This effectively disables the Automatic Addressing mode and
allows the microcontroller to use standard 80C51 type UART drivers
which do not make use of this feature.
SCON Address = 98H
Reset Value = 0000 0000B
SM0/FE SM1 SM2 REN TB8 RB8 Tl Rl
Bit Addressable
(SMOD0 = 0/1)*
Symbol Function
FE Framing Error bit. This bit is set by the receiver when an invalid stop bit is detected. The FE bit is not cleared by valid
frames but should be cleared by software. The SMOD0 bit must be set to enable access to the FE bit.
SM0 Serial Port Mode Bit 0, (SMOD0 must = 0 to access bit SM0)
SM1 Serial Port Mode Bit 1
SM0 SM1 Mode Description Baud Rate**
0 0 0 shift register f
OSC
/12
0 1 1 8-bit UART variable
1 0 2 9-bit UART f
OSC
/64 or f
OSC
/32
1 1 3 9-bit UART variable
SM2 Enables the Automatic Address Recognition feature in Modes 2 or 3. If SM2 = 1 then Rl will not be set unless the
received 9th data bit (RB8) is 1, indicating an address, and the received byte is a Given or Broadcast Address.
In Mode 1, if SM2 = 1 then Rl will not be activated unless a valid stop bit was received, and the received byte is a
Given or Broadcast Address. In Mode 0, SM2 should be 0.
REN Enables serial reception. Set by software to enable reception. Clear by software to disable reception.
TB8 The 9th data bit that will be transmitted in Modes 2 and 3. Set or clear by software as desired.
RB8 In modes 2 and 3, the 9th data bit that was received. In Mode 1, if SM2 = 0, RB8 is the stop bit that was received.
In Mode 0, RB8 is not used.
Tl Transmit interrupt flag. Set by hardware at the end of the 8th bit time in Mode 0, or at the beginning of the stop bit in the
other modes, in any serial transmission. Must be cleared by software.
Rl Receive interrupt flag. Set by hardware at the end of the 8th bit time in Mode 0, or halfway through the stop bit time in
the other modes, in any serial reception (except see SM2). Must be cleared by software.
NOTE:
*SMOD0 is located at PCON6.
**f
OSC
= oscillator frequency
SU00043
Bit: 76543210
Figure 7. SCON: Serial Port Control Register
