12.4.3.2 Primary Oscillator Pin Functionality

The POSC pins (OSCI and OSCO) can be used for other functions when the oscillator is not being used. The POSCMD[1:0] bits in the Oscillator Configuration register (OSCCFG) determine the oscillator pin function. The POSCIOFNC bit (OSCCFG) determines the OSCO pin function.

POSCMD[1:0]: Primary Oscillator Mode Selection bits:

  • 11 = Off (Enables GPIO on CLKI pin)
  • 10 = High-Frequency mode (HS 10-32 MHz)
  • 01 = Primary Oscillator: Medium Frequency mode (XT 0-10 MHz)
  • 00 = External Clock mode (EC)

POSCIOFNC: OSCO Pin Function bit (except in XT and HS modes):

  • 1 = OSCO is the clock output, and the instruction cycle (FCY) clock is output on the OCSO pin (see Figure 12-7).
  • 0 = OSCO is a general purpose digital I/O pin.

The oscillator pin functions are provided in Table 12-7.

Table 12-7. Clock Pin Function Selection
Oscillator SourcePOSCIOFNC ValuePOSCMD[1:0] ValueOSCI

Pin Function(1)

OSCO

Pin Function(2)

POSC 
Disabled111Digital I/OClock Output
POSC 
Disabled011Digital I/ODigital I/O
HSx10OSCIOSCO
XTx01OSCIOSCO
EC100OSCIClock Output
EC000—Digital I/O
Note:
  1. OSCI pin function is determined by the Primary Oscillator Mode Selection (POSCMOD[1:0]) 
Configuration bits.
  2. OSCO pin function is determined by the Primary Oscillator Mode Selection (POSCMOD[1:0]), OSCIOFNC Configuration bits.
Figure 12-7. OSCO Pin for Clock Output (in EC Mode)