AT87C5112 View Datasheet(PDF) - Atmel Corporation
Part Name
Description
Manufacturer
AT87C5112 Datasheet PDF : 97 Pages
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Power-down Modes
Prescaler Divider
4191C–8051–02/08
AT8xC5112
• Exit from IDLE modes will leave the oscillator control bits OSCAEN, OSCBEN and
CKS unchanged.
• POWER-DOWN modes are achieved by using any instruction that writes into
PCON.1 sfr
• Exit from POWER-DOWN mode is achieved either by a hardware Reset, or by an
external interruption.
• By RST signal: The CPU will restart on OSCA.
• By INT0 or INT1 interruptions, if enabled. The oscillators control bits OSCAEN,
OSCBEN and CKS will not be changed, so the selected oscillator before entering
into Power-down will be activated.
Table 1. Power Modes
PD IDLE CKS OSCBEN OSCAEN Selected Mode Comment
0
0
1
X
1 NORMAL MODE A OSCA: XTAL clock
X
X
1
X
0 INVALID
No active clock
0
0
0
1
X NORMAL MODE B OSCB: high-speed RC clock
X
X
0
0
X INVALID
0
1
1
X
1 IDLE MODE A
The CPU is off, OSCA supplies the
peripherics
0
1
0
1
X IDLE MODE B
The CPU is off, OSCB supplies the
peripherics
1
X
X
X
X
TOTAL POWER- The CPU is off, OSCA and OSCB are
DOWN
stopped
• An hardware RESET selects the prescaler divider:
– CKRL = FFh: internal clock = OscOut/2 (Standard C51 feature)
– X2 = 0,
• After Reset, any value between FFh down to 00h can be written by software into
CKRL sfr in order to divide frequency of the selected oscillator:
– CKRL = 00h: minimum frequency = OscOut/512
– CKRL = FFh: maximum frequency = OscOut/2
The frequency of the CPU and peripherals clock CkOut is related to the frequency of the
main oscillator OscOut by the following formula:
FCkOut = FOscOut/(512 - 2*CKRL)
Some examples can be found in the table below:
FOscOut
MHz
12
X2
CKRL
0
FF
FCkOut (Mhz)
6
12
0
FE
3
12
1
x
12
• A software instruction which sets X2 bit de-activates the prescaler/divider, so the
internal clock is either Xtal_Osc or RC_Osc depending on SEL_OSC bit.
9
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