I've been in that predicament myself before with mortgage payments and had to pay only half the mortgage payment that month but I spoke to the bank beforehand and since I was always on time with the mortgage payments and it only happened those few times they didn't hit me with late charges or try to foreclose on the mortgage.
What I did though was make the rest of the payment for the mortgage with the next months payment and everything was okay.
But it can depend on your banks policies and how you've been with making the monthly mortgage payments.
When you sign a mortgage agreement you're agreeing that you will make all mortgage payments in full on time so they could mark you down as being late on the mortgage payment even though you've made half the mortgage payment.
If your mortgage payment is due though and you can only pay half the payment before the due date then can pay the rest of the mortgage payment another week when you get paid again then that should be okay as well.