8 Sep 2010 9:18:17
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Common Problems |
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Why can't I get P1.2 into quasi I/O or push-pull output mode? |
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This note applies to the PDS900 emulation system.
PDS900 uses a P89LPC935 bondout device to emulate all members of the LPC900 family. As the P89LPC935 device has an I2C interface, the pins that interface with the I2C subsystem (P1.2 and P1.3) are necessarily open-drain outputs. They cannot be configured as quasi I/O or push-pull mode outputs as the requisite hardware does not exist on those port pins on a P89LPC935.
This presents some limitations when you are emulating devices that implement P1.2 but do not have an I2C interface (currently only the P89LPC901, P89LPC907, P89LPC912 and P89LPC914 devices). These devices are capable of operating P1.2 in quasi I/O or push-pull mode, but PDS900 will ignore any attempts to program P1.2 into these modes as the P89LPC935 bondout does not support it.
This limitation would also apply to any device that implements P1.3 and does not have an I2C interface, however there are currently no such devices in the P89LPC900 family.
Note that this is an inherent limitation of the Philips bondout devices and there is no work-around. All emulators for the P89LPC900 family (regardless of vendor) suffer from this limitation.
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