PIC 16F684 - I can't simulate an external oscillator for TMR1 with MPLAB SIM

I have MPLAB V8.73 and I'm using MPLAB SIM to simulate a programme I wrote for a PIC 16F684.

I want to drive TMR1 with a 32.768 kHz crystal.

But when I try to simulate this situation, TMR1 does not change.

I set _INTOSC_OSC_NOCLKOUT in the configuration and the following bits in the programme:-

PIE1, TMR1IE

INTCON, PEIE

T1CON, TMR1CS; T1CON, T1OSCEN & T1CON, TMR1ON

I'm using PIR1, TMR1IF to determine when an overflow of TMR1 occurs.

I setup the Clock Stimulus as shown in the attachment.

What am I missing?

Any advice will be appreciated.

Len