Freescale Semiconductor MC68HC908MR32 Manual Do Utilizador
Timer Interface B (TIMB)
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
238
Freescale Semiconductor
17.3.1 TIMB Counter Prescaler
The TIMB clock source can be one of the seven prescaler outputs or the TIMB clock pin,
PTE0/TCLKB
.
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.
in the TIMB status and control register select the TIMB clock source.
17.3.2 Input Capture
An input capture function has three basic parts:
1.
Edge select logic
2.
Input capture latch
3.
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–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,
TCHxH–TCHxL. 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.
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–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,
TCHxH–TCHxL. 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 status and control register
(TBCHxH–TBCHxL, see
(TBCHxH–TBCHxL, see
) on each proper signal transition regardless of
$0056
TIMB Channel 0 Status/Control
Register
Read:
CH0F
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
Write:
0
Reset:
0
0
0
0
0
0
0
0
$0057
TIMB Channel 0 Register High
(TBCH0H)
Read:
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
Write:
Reset:
Indeterminate after reset
$0058
TIMB Channel 0 Register Low
(TBCH0L)
Read:
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Write:
Reset:
Indeterminate after reset
$0059
TIMB Channel 1 Status/Control
Register
Read:
CH1F
CH1IE
0
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
Write:
0
R
Reset:
0
0
0
0
0
0
0
0
$005A
TIMB Channel 1 Register High
(TBCH1H)
Read:
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
Write:
Reset:
Indeterminate after reset
$005B
TIMB Channel 1 Register Low
(TBCH1L)
Read:
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Write:
Reset:
Indeterminate after reset
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
R
= Reserved
Figure 17-3. TIMB I/O Register Summary (Continued)