AT89C5122 ATMEL [ATMEL Corporation], AT89C5122 Datasheet - Page 49

• Manufacturer Part Number: AT89C5122
• Description: MICROCONTROLLER WITH USB AND SMART CARD READER INTERFACES
• Manufacturer: ATMEL [ATMEL Corporation]

Alternate Card Clock
DC/DC Converter Clock
4202D–SCR–06/05
If the CK_CPU <= 4/3 * CK_ISO, the SCIB doesn’t work.
If the CK_CPU >= 6* CK_ISO, the programmer must take care in three cases:
•
•
•
To avoid any trouble, a delay must be added between the two accesses on the SCIB
register. The SCIB must complete the first read (or write) operation before to receive the
second. A solution is to add NOP (no operation) instructions. The number of NOP to add
depends of the rate between CK_CPU and CK_ISO (see table below).
The alternate Card uses the peripheral clock divided by the PR3 prescaler. (1; 1/2; 1/4;
1/8 division ratio). See Section "Alternate Card", page 78 for the definition of the alter-
nate clock.
The DC/DC block needs a clock with a 50% duty cycle. The frequency must also be
included in the range 3.68 MHz and 6 MHz. The PR4 prescaler is used to configure the
DC/DC frequency.
Linked registers
Write in SCICR and after read of SCETU0-1
Write in SCIBUF and after read of SCISR
Wait after Write operation on this registers
SCICR, SCIER, SCETU0-1,SCGT0-1,
SCWT0-3,SCCON
Min CLK_CPU
CLK_CPU >= 6 * CLK_ISO
CLK_CPU >= 12* CLK_ISO
XTAL1 (MHz)
Read (or write) operation on a SCIB register followed immediatly with an other Read
(or write) operation on the same register.
Read (or write) operation on a SCIB register followed immediatly with an other Read
(or write) operation on a linked register. The list of linked registers is in the table
below.
Write operation on a register of the list below followed immediatly with a read
operation on a SCIB register.
8
DCCKPS3:0 value
0
Max CLK_CPU
CLK_CPU <= 12 * CLK_ISO
CLK_CPU <= 16 * CLK_ISO
Prescaler Factor
2
DC/DC converter CLK (MHz)
Number of
CPU cycles to add
6 ( example1 NOP)
12 ( example 2 NOP)
4
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