89C5121-SK1 Atmel, 89C5121-SK1 Datasheet - Page 27

• Manufacturer Part Number: 89C5121-SK1
• Description: KIT SMART CARD FOR AT89C5121
• Manufacturer: Atmel
• Type: Smart Cardr

Specifications of 89C5121-SK1

• Contents: Board
• For Use With/related Products: AT89C5121
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: T89C5121-SK1; T89C5121-SK1

DC/DC Clock
Clock Control Register
Clock Prescaler
4164G–SCR–07/06
The DC/DC block needs a clock with a 50% duty cycle. The frequency must also respect
a value between 3.68 MHz and 4 MHz. The first requirement imposes a divider in the
clock path and the second constraint is solved with the use of a prescaler.
Figure 13. Functional Block Diagram
This register is used to reload the clock prescaler of the DC/DC converter clock.
Table 11. DCCKPS Register
DCCKPS - DC/DC converter Reload Register (BFh)
Reset Value = XXXX XX11b
Before supplying the DC/DC block, the oscillator clock is divided by a factor 2 to 5 to
adapt the clock needed by the DC/DC converter. This factor is controlled with the
DCCKPS register.
The prescaler factor must be chosen to match the requirement range which is 4MHz.
Table 12. Examples of Factors
Number
Bit
7:2
1:0
XTAL (MHz)
7
-
14.756
12
16
20
8
Mnemonic
DCCKPS
Bit
-
6
-
F
OSC
Description
Reserved
Do not use write those bits
Clock Reload Register
Prescaler value
00b: Division factor equals 2
01b: division factor equals 3
10b: division factor equals 4
11b: division factor equals 5 (reset value which minimize the consumption)
DCCKPS Value
5
-
00h
01h
02h
02h
03h
(2 to 5)
DCCKPS
Address BFh
1
4
-
Prescaler
Factor
2
3
4
4
5
3
-
F
2 to 5
OSC
2
-
DC/DC Converter CLK (MHz)
A/T8xC5121
F
CLK_DC/DC
DCCKPS
1
3.689
4
4
4
4
DCCKPS
0
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