AN2556 datasheet(20/35 Pages) STMICROELECTRONICS

20 / 35 page

New features

AN2556

20/35

2.2.1

Hardware impacts

None.

2.2.2

Software impacts

None, if only CLKOUT is needed.

When the CLKOUT function is enabled by setting the CLKEN bit of register SYSCON, CPU

clock output is on P3.15 by default.

To access the XCLKOUTDIV register and thus program the clock prescaling factor, the

XMISCEN bit of XPERCON and XPEN of the SYSCON registers must be set.

2.3

New multiplexer for X-Interrupts

The limited number of XBus interrupt lines of the present ST10 architecture imposes some

constraints on the implementation of new functionalities. In particular, the additional

XPeripherals XSSC, XASC, XI2C and XPWM need some resources to implement interrupt

and PEC transfer. For this reason, a complex but very flexible multiplexed structure for

interrupt is suggested. In Figure 2: X-Interrupt basic structure the principle is represented

through a simple diagram, which shows the basic structure replicated for each of the four X-

interrupt vectors (XP0INT, XP1INT, XP2INT and XP3INT).

It is based on a new 16-bit register XIRxSEL (x = 0,1,2,3), divided in two portions:

●

Byte High (XIRxSEL[15:8]) Interrupt Enable bits

●

Byte Low (XIRxSEL[7:0]) Interrupt Flag bits

AN2556 Datasheet(PDF) 20 Page - STMicroelectronics