Rainbow-electronics AT89C5132 Instrukcja Użytkownika Pobierz pdf (Strona 107)

107

AT8xC5132

4173A–8051–08/02

Serial I/O Port The serial I/O port in the AT8xC5132 provides both synchronous and asynchronous

communication modes. It operates as a Synchronous Receiver and Transmitter in one

single mode (Mode 0) and operates as an Universal Asynchronous Receiver and Trans-

mitter (UART) in three full-duplex modes (modes 1, 2 and 3). Asynchronous modes

support framing error detection and multiprocessor communication with automatic

address recognition.

Mode Selection SM0 and SM1 Bits in SCON register (see Figure 107) are used to select a mode among

the single synchronous and the three asynchronous modes according to Table 105.

Table 105. Serial I/O Port Mode Selection

Baud Rate Generator Depending on the mode and the source selection, the baud rate can be generated from

either the Timer 1 or the Internal Baud Rate Generator. The Timer 1 can be used in

Modes 1 and 3 while the Internal Baud Rate Generator can be used in Modes 0, 1

and 3.

The addition of the Internal Baud Rate Generator allows freeing of the Timer 1 for other

purposes in the application. It is highly recommended to use the Internal Baud Rate

Generator as it allows higher and more accurate baud rates than Timer 1.

Baud rate formulas depend on the modes selected and are given in the following mode

sections.

Timer 1 When using Timer 1, the Baud Rate is derived from the overflow of the timer. As shown

in Figure 76 Timer 1 is used in its 8-bit auto-reload mode (detailed in Section "Mode 2

(8-bit Timer with Auto-Reload)", page 52). SMOD1 bit in PCON register allows doubling

of the generated baud rate.

Figure 76. Timer 1 Baud Rate Generator Block Diagram

SM0 SM1 Mode Description Baud Rate

0 0 0 Synchronous Shift Register Fixed/Variable

0 1 1 8-bit UART Variable

1 0 2 9-bit UART Fixed

1 1 3 9-bit UART Variable

TR1

TCON.6

GATE1

TMOD.7

Overflow

C/T1#

TMOD.6

TL1

(8 Bits)

TH1

(8 Bits)

INT1#

PER

CLOCK

÷ 6

SMOD1

PCON.7

÷ 2

CLOCK

To Serial Port

1 2 ... 102 103 104 105 106 107 108 109 110 111 112 ... 161 162

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