Rainbow-electronics T89C51AC2 Manuel d'utilisateur télécharger pdf (Page 17)

17

T89C51AC2

Rev. B – 19-Dec-01

Figure 6. Mode Switching Waveforms

Note: In order to prevent any incorrect operation while operating in the X2 mode, users must be

aware that all peripherals using the clock frequency as a time reference (UART, timers...)

will have their time reference divided by two. For example a free running timer generating

an interrupt every 20 ms will then generate an interrupt every 10 ms. A UART with a

4800 baud rate will have a 9600 baud rate.

6.2 Register Table 12. CKCON Register

CKCON (S:8Fh)

Clock Control Register

XTAL2

XTAL1

CPU clock

X2 bit

X2 ModeSTD Mode STD Mode

76543210

- WDX2 PCAX2 SIX2 T2X2 T1X2 T0X2 X2

Bit

Number

Bit

Mnemonic Description

6WDX2

Watchdog clock (1)

Clear to select 6 clock periods per peripheral clock cycle.

Set to select 12 clock periods per peripheral clock cycle.

5 PCAX2

Programmable Counter Array clock (1)

Clear to select 6 clock periods per peripheral clock cycle.

Set to select 12 clock periods per peripheral clock cycle.

4SIX2

Enhanced UART clock (MODE 0 and 2) (1)

Clear to select 6 clock periods per peripheral clock cycle.

Set to select 12 clock periods per peripheral clock cycle.

3T2X2

Timer2 clock (1)

Clear to select 6 clock periods per peripheral clock cycle.

Set to select 12 clock periods per peripheral clock cycle.

2T1X2

Timer1 clock (1)

Clear to select 6 clock periods per peripheral clock cycle.

Set to select 12 clock periods per peripheral clock cycle.

1T0X2

Timer0 clock (1)

Clear to select 6 clock periods per peripheral clock cycle.

Set to select 12 clock periods per peripheral clock cycle.

1 2 ... 12 13 14 15 16 17 18 19 20 21 22 ... 109 110

T89C51AC2 1

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