Timer Interface Module B (TIMB)
MC68HC08AZ32A Data Sheet, Rev. 2
258
Freescale Semiconductor
18.3.1 TIMB Counter Prescaler
The TIMB clock source can be one of the seven prescaler outputs or the TIMB clock pin,
PTD4/ATD12/TBCLK. The prescaler generates seven clock rates from the internal bus clock. The
prescaler select bits, PS[2:0], in the TIMB status and control register select the TIMB clock source.
18.3.2 Input Capture
An input capture function has three basic parts: edge select logic, an input capture latch and a 16-bit
counter. Two 8-bit registers, which make up the 16-bit input capture register, are used to latch the value
of the free-running counter after the corresponding input capture edge detector senses a defined
transition. The polarity of the active edge is programmable. The level transition which triggers the counter
transfer is defined by the corresponding input edge bits (ELSxB and ELSxA in TBSC0 through TBSC1
control registers with x referring to the active channel number). When an active edge occurs on the pin of
an input capture channel, the TIMB latches the contents of the TIMB counter into the TIMB channel
registers, TBCHxH–TBCHxL. Input captures can generate TIMB CPU interrupt requests. Software can
determine that an input capture event has occurred by enabling input capture interrupts or by polling the
status flag bit.
The free-running counter contents are transferred to the TIMB channel register (TBCHxH–TBCHxL, see
flag (CH0F–CH1F in TBSC0–TBSC1 registers) is set or clear. When the status flag is set, a CPU interrupt
is generated if enabled. The value of the count latched or “captured” is the time of the event. Because this
value is stored in the input capture register 2 bus cycles after the actual event occurs, user software can
$0045
Timer B Channel 0 Status
and Control Register
Read:
CH0F
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
Write:
0
Reset:
0
$0046
Timer B Channel 0 Register
High (TBCH0H)
Read:
Bit 15
14
13
12
11
10
9
Bit 8
Write:
Reset:
Indeterminate after reset
$0047
Timer B Channel 0 Register
Low (TBCH0L)
Read:
Bit 7
6
5
4
3
2
1
Bit 0
Write:
Reset:
Indeterminate after reset
$0048
Timer B Channel 1 Status
and Control Register
Read:
CH1F
CH1IE
0
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
Write:
0R
Reset:
0
$0049
Timer B Channel 1 Register
High (TBCH1H)
Read:
Bit 15
14
13
12
11
10
9
Bit 8
Write:
Reset:
Indeterminate after reset
$004A
Timer B Channel 1 Register
Low (TBCH1L)
Read:
Bit 7
6
5
4
3
2
1
Bit 0
Write:
Reset:
Indeterminate after reset
Addr.
Name
Bit 7
6
5
4
3
2
1
Bit 0
= Unimplemented
R
= Reserved
Figure 18-3. TIMB I/O Register Summary (Continued)