Rainbow Electronics AT89C5122 - Manual (Page 49)

49
AT8xC5122/23
4202E–SCR–06/06
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:
• 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.
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).
Alternate Card Clock 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.
DC/DC Converter 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 Max CLK_CPU
Number of
CPU cycles to add
CLK_CPU >= 6 * CLK_ISO CLK_CPU <= 12 * CLK_ISO 6 ( example1 NOP)
CLK_CPU >= 12* CLK_ISO CLK_CPU <= 16 * CLK_ISO 12 ( example 2 NOP)
XTAL1 (MHz) DCCKPS3:0 value Prescaler Factor DC/DC converter CLK (MHz)
8 0 2 4