MC68HC05L16 Datasheet, PDF (81/146 Pages) Freescale Semiconductor, Inc – Microcontrollers

Timer 1
IEDG — Input Edge
The value of the input edge determines which level transition on the TCAP pin will trigger free-running
counter transfer to the input capture register.
Reset does not affect the IEDG bit.
0 = Negative edge
1 = Positive edge
Bits 2–4 — Not Used
Always read logic 0
OLVL — Not Used
Always read logic 0
9.2.5 Timer Status Register
The TSR is a read-only register containing three status flag bits.
Address: $0013
Bit 7
6
5
4
3
2
1
Bit 0
Read: ICF
OC1F
TOF
0
0
0
0
0
Write:
Reset: U
U
U
0
0
0
0
0
= Unimplemented
U = Unaffected
Figure 9-4. Timer Status Register (TSR)
ICF — Input Capture Flag
0 = Flag cleared when TSR and input capture low register ($15) are accessed
1 = Flag set when selected polarity edge is sensed by input capture edge detector
OC1F — Output Compare 1 Flag
0 = Flag cleared when TSR and output compare low register ($17) are accessed
1 = Flag set when output compare register contents match the free-running counter contents
TOF — Timer Overflow Flag
0 = Flag cleared when TSR and counter low register ($19) are accessed
1 = Flag set when free-running counter transition from $FFFF to $0000 occurs
Bits 0–4 — Not Used
Always read logic 0
Accessing the timer status register satisfies the first condition required to clear status bits. The remaining
step is to access the register corresponding to the status bit.
A problem can occur when using the timer overflow function and reading the free-running counter at
random times to measure an elapsed time. Without incorporating the proper precautions into software,
the timer overflow flag could unintentionally be cleared if:
1. The timer status register is read or written when TOF is set.
2. The LSB of the free-running counter is read but not for the purpose of servicing the flag.
The counter alternate register at address $1A and $1B contains the same value as the free-running
counter (at address $18 and $19); therefore, this alternate register can be read at any time without
affecting the timer overflow flag in the timer status register.
MC68HC05L16 • MC68HC705L16 Data Sheet, Rev. 4.1
Freescale Semiconductor
81