UPSD3422 datasheet(95/293 Pages) STMICROELECTRONICS

95 / 293 page

uPSD34xx

Standard 8032 timer/counters

95/293

The timer can be configured for either “timer” or “counter” operation. In the most typical

applications, it is configured for “timer” operation (C/T2 = 0). “Timer” operation is a little

different for Timer 2 when it's being used as a baud rate generator. In this case, the baud

rate is given by the formula:

UART Mode 1,3 Baud Rate =fOSC/(32 x [65536 – [RCAP2H, RCAP2L]))

where [RCAP2H, RCAP2L] is the content of the SFRs RCAP2H and RCAP2L taken as a

16-bit unsigned integer.

A roll-over in TH2 does not set TF2, and will not generate an interrupt. Therefore, the Timer

Interrupt does not have to be disabled when Timer 2 is in the Baud Rate Generator Mode.

If EXEN2 is set, a 1-to-0 transition on pin T2X will set the Timer 2 interrupt flag EXF2, but

will not cause a reload from RCAP2H and RCAP2L to TH2 and TL2. Thus when Timer 2 is

in use as a baud rate generator, the pin T2X can be used as an extra external interrupt, if

desired.

When Timer 2 is running (TR2 = 1) in a “timer” function in the Baud Rate Generator Mode,

firmware should not read or write TH2 or TL2. Under these conditions the results of a read

or write may not be accurate. However, SFRs RCAP2H and RCAP2L may be read, but

should not be written, because a write might overlap a reload and cause write and/or reload

errors. Timer 2 should be turned off (clear TR2) before accessing Timer 2 or Registers

RCAP2H and RCAP2L, in this case.

Table 45 on page 96 shows commonly used baud rates and how they can be obtained from

Timer 2, with T2CON = 34h.

UPSD3422 датащи(PDF) 95 Page - STMicroelectronics