ST9 datasheet(130/146 Pages) STMICROELECTRONICS

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ST9 USER GUIDE

5.5.3 Port Initialisation

When you have configured all the peripherals as described above, you should initialise the

ports to your requirements: input or output, open drain or push-pull, TTL or CMOS levels, etc.

for the parallel I/O ports.

You must set the port pins that serve as inputs or outputs for peripherals as either:

– Alternate Function for peripheral outputs, or

– Regular Input for peripheral inputs

The exception is the A/D converter, where you must set the input pin as Alternate Function.

5.5.4 Final Initialisation

Install the Working Registers in the group defined for the main program.

Set the Page Pointer Register to a default value.

Set the Global Counter Enable, the global Interrupt ENable and, if required the Watchdog

function.

The main program is now ready to run.

5.6 INTERRUPT CONSIDERATIONS

The ST9 has two main paging registers:

– The RPP register pair that selects the working register group

– The PPR register that selects one of 256 pages within register group 15

These registers are essential to the correct working of the program.

When an interrupt occurs, it is likely you will have to change either or both of these registers.

This is why you must push them to the stack on entry, and pop them back on exit.

An interrupt is requested by a bit in a register of a peripheral. This bit is not reset automatically

by the fact that the interrupt is serviced. You must reset it in the code of your interrupt service

routine.

If you write an interrupt service routine in C, by default PPR and all registers used by the rou-

tine are pushed on the stack. This can be time-consuming. If your program is entirely written

in C, and you use none or few registers explicitly, the register file has enough room to allocate

a private working register group for each interrupt service routine. You specify this by a

#pragma pseudo-instruction. This method provides the fastest response times.

ST9 Datasheet(PDF) 130 Page - STMicroelectronics