but looking through the datasheet reveals no

Phi eh NXP divides the information between a device datasheet and a fsmily user manual.

the user manual which it is essential for you to have reveal

Table 24: Port output configuration settings
PxM1.y PxM2.y Port output mode
0      0      Quasi-bidirectional
0      1      Push-pull
1      0      Input only (high-impedance)
1      1      Open drain

Erik

PS
if you define the port pins by names (which I do hope you do) I suggest that you do something like this in the module defining the names

P0pp = (x + y + z) ; ports pushpull or open drain
P0i0 = ( a + c + z); ports input only or open drain

and then in the init code

P0M1 = P0pp
P0M2 = P0od

I find that so uch easier to spot errors in than

P0M1=0x8a;
P0M2=0x45;