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Programmable Interval Timer Registers
élanSC520 Microcontroller Register Set Manual
13-11
PIT Read-Back Command (PITRDBACK)
Direct-Mapped
I/O Address 0043h
Register Description
This register allows the status and current count of each channel to be read.
Bit Definitions
7
6
5
4
3
2
1
0
Bit
CTR_SEL[1–0]
LCNT
LSTAT
CNT2
CNT1
CNT0
Reserved
Reset
0
0
0
W
0
W
0
W
0
W
0
W
0
R/W
W
RSV
Bit
Name
Function
7–6
CTR_SEL[1–0]
PIT Counter Select/Read
-
back Command
When this address (Port 0043h) is written with bits 7–6 = 11b, the PITRDBACK register
is addressed, and this CTR_SEL bit field invokes the read-back command.
00–10 = The PITMODECTL or PITCNTLAT register is addressed (see page 13-7 and
page 13-10).
11 = Read-back command: the values selected by bits 5–1 of this register are made
available to be read back from the PITxCNT registers (see the descriptions starting
on page 13-2) immediately following completion of the I/O write that invokes this
read-back command.
Latched counts are read back from the PITxCNT registers (see the descriptions starting
on page 13-2) based on the current read/write mode selected for each counter via the
CTR_RW_LATCH bit field of the PITMODECTL register (see page 13-7). The latched
status bytes are returned in the PITxSTA register format (see page 13-5).
If both LSTAT and LCNT = 0b, the status byte is made available at the respective
PITxCNT register first. When this byte has been read, the latched count bytes are made
available, bits 7–0 first, and then bits 15–8 (if the channel is set up to read back all 16
bits of count via the CTR_RW_LATCH bit field of the PITMODECTL).
When this address (Port 0043h) is written with bits 7–6
11b and bits 5–4
00b, this
address is redefined (for the duration of the current I/O write) as the PITMODECTL
register (see page 13-7)
When this address (Port 0043h) is written with bits 7–6
11b, and bits 5–4 = 00b, this
address is redefined (for the duration of the current I/O write) as the PITCNTLAT register
(see page 13-10).
5
LCNT
Latch Count (Low True)
0 =Latch count data for the counters selected via bits CNT2–CNT0.
1 =Do not latch count data for the counters selected via bits CNT2–CNT0.
4
LSTAT
Latch Status (Low True)
0 =Latch the status byte for the counters selected via bits CNT2–CNT0.
1 =Do not latch the status byte for the counters selected via bits CNT2–CNT0.
3
CNT2
Select Counter 2
0 =Counter 2 is not selected for operations specified by bits LCNT and LSTAT.
1 =Counter 2 is selected for operations specified by bits LCNT and LSTAT.
2
CNT1
Select Counter 1
0 =Counter 1 is not selected for operations specified by bits LCNT and LSTAT.
1 =Counter 1 is selected for operations specified by bits LCNT and LSTAT.
1
CNT0
Select Counter 0
0 =Counter 0 is not selected for operations specified by bits LCNT and LSTAT.
1 =Counter 0 is selected for operations specified by bits LCNT and LSTAT.