Lpc2000

On 4 Jan 2005 at 14:06, Aalt Lokhorst wrote:

> 
> Hello All,
> 
> In the Philips document 'UM_LPC21XX_LPC22XX_2.pdf' on page 137 I read:
> 
>    Applications that require instanatneous appearance of zeros and
>    ones on the respected parallel port can use direct access to port’s
>    corresponding GPIO Pin Value Register (IOPIN). Assuming that pins
>    P0.8 to P0.15 are configured as output, write to IO0PIN:
> 
>      IO0PIN = 0x0000 C700
> 
>    will produce the same output as following sequence of writes:
> 
>      IO0SET = 0x0000 C700
>      IO0CLR = 0x0000 3800
> 
>    Solution utilizing access to IO0SET and IO0CLR will take more steps
>    compared to a single IO0PIN write access.
> 
> The same document shows on page 135 that IO#PIN is a ReadOnly
> register.
> 
> Am I missing something, how can you write to a ReadOnly register?
> 

Have you received any feedback on this from Philips ? I also notice that 
IOSET is defined as Read/Write. Why would one want to read the IOSET
register. As far as I understand it, If one writes 1 to IOSET, then 1 to IOCLR,
the output pin would be 0, but the IOSET register will still indicate a 1, hence
making a read from this register meaningless.

Regards
   Anton Erasmus



-- 
A J Erasmus