Maxim Integrated Secure Microcontroller - Manual (Page 126)

Secure Microcontroller User’s Guide
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Table 14-C. Serial I/O Operating Modes
MODE SYNC/ASYNC BAUD CLOCK DATA BITS START/STOP
9TH DATA BIT
FUNCTION
MODE 0 SYNC 12 t
CLK
8 None None
MODE 1 ASYNC Timer 1 8 1 Start None
Overflow 1 Stop
MODE 2 ASYNC 32 t
CLK
or 9 1 Start 0, 1, or parity
64 t
CLK
1 Stop
MODE 3 ASYNC Timer 1 9 1 Start 0, 1, or parity
Overflow 1 Stop
The serial port is controlled by the SCON register. Serial interrupts are also used, which are controlled by
IE and IP. The setup for each SFR is shown below. In addition, Mode 1 is associated with Timer 1, which
is controlled by TCON and TMOD.
Mode 1 is selected using the SCON register. The table from the SCON register shown below indicates
that Mode 1 is selected by choosing the value SM0 = 0 and SM1 = 1.
SM0 SM1 MODE FUNCTION WORD LENGTH BAUD CLOCK
0 0 Mode 0 Synchronous 8 bits 12 t
CLK
0 1 Mode 1 Asynchronous 10 bits Timer 1 Overflow
1 0 Mode 2 Asynchronous 11 bits 32 t
CLK
or 64 t
CLK
1 1 Mode 3 Asynchronous 11 bits Timer 1 Overflow
SM0 = 0 and SM1 = 1 corresponds to the value SCON.7 = 0 and SCON.6 = 1. In addition, since the
application must receive data, the serial receiver must be enabled. This is done by setting the REN bit at
SCON.4 to a logic 1. The remaining bits in SCON can be written to 0. Thus the value for SCON is 50h.
SCON–98h
SM0 SM1 SM2 REN TB8 RB8 TI RI
0 1 0 1 0 0 0 0
This application uses the serial interrupt, which serves two purposes. First, the software knows when a
byte has been sent, so it knows when another can be written. Second, after the 256 bytes have been
transmitted, the PC will respond. It is not known when this occurs, and the software may have other tasks
to attend. Therefore, the serial interrupt will inform the microcontroller when the confirmation code has
been received by the serial port. This example enables only the serial interrupt. It is set for high priority
since other interrupts might be enabled in a real system.
IE–0A8h
EA — — ES ET1 EX1 ET0 EX0
1 0 0 1 0 0 0 0