Interrupt

This is probably pretty basic, but I can't figure out why it doesn't work.

I am working with a MSC1211Y5 evaluation board, and I am trying to
test the serial interrupts on the board. I feel like I've written
what I need to trigger an interrupt, but it doesn't enter into my
interrupt function (this is programmed in C). I'm still pretty new
to this (as you can see) and haven't found the resources to help me
with this. Shouldn't the following code trigger a serial interrupt?

void main ( void ) {

REN_0 = 1;
TB8_0 = 1;
SM0_0 = 1;
SM1_0 = 0;
TI_0 = 0;
TH1 = -3;
ES = 1;
EA = 1;

while (1) {
SBUF = 0x88;
} }

Basically, I feel that it should enter an interrupt whenever SBUF is
written to, right? Because the T1 flag should get set. My interrupt
is named like this:

void serial_isr (void) interrupt 1

I tested if the T1 flag gets set by doing:
while (1) {
SBUF = 0x88;
if (T1 == 1) serial_isr();
}

and it worked! (I removed the "interrupt 1" sign next to the second function). So I'm not sure what I didn't set.

Thanks in advance for any help.