Rainbow Electronics T89C51AC2 - Manual (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 Mode STD Mode STD Mode
7 6 5 4 3 2 1 0
- WDX2 PCAX2 SIX2 T2X2 T1X2 T0X2 X2
Bit
Number
Bit
Mnemonic Description
6 WDX2
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.
4 SIX2
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.
3 T2X2
Timer2 clock (1)
Clear to select 6 clock periods per peripheral clock cycle.
Set to select 12 clock periods per peripheral clock cycle.
2 T1X2
Timer1 clock (1)
Clear to select 6 clock periods per peripheral clock cycle.
Set to select 12 clock periods per peripheral clock cycle.
1 T0X2
Timer0 clock (1)
Clear to select 6 clock periods per peripheral clock cycle.
Set to select 12 clock periods per peripheral clock cycle.