cop888eb National Semiconductor Corporation, cop888eb Datasheet - Page 15

• Manufacturer Part Number: cop888eb
• Description: 8-bit Cmos Rom Based Microcontrollers With 8k Memory, Can Interface, 8-bit A/d, And Usart
• Manufacturer: National Semiconductor Corporation

Control Registers
The ICNTRL register contains the following bits:
Reserved This bit is reserved and should be zero
T2CNTRL Register (Address X'00C6)
The T2CNTRL control register contains the following bits:
Timers
The device contains a very versatile set of timers (T0, T1 and
T2). All timers and associated autoreload/capture registers
power up containing random data.
TIMER T0 (IDLE TIMER)
The device supports applications that require maintaining
real time and low power with the IDLE mode. This IDLE
mode support is furnished by the IDLE timer T0, which is a
16-bit timer. The Timer T0 runs continuously at the fixed rate
of the instruction cycle clock, t
write to the IDLE Timer T0, which is a count down timer.
The Timer T0 supports the following functions:
Figure 8 is a functional block diagram showing the structure
of the IDLE Timer and its associated interrupt logic.
Bits 11 through 15 of the ITMR register can be selected for
triggering the IDLE Timer interrupt. Each time the selected
bit underflows (every 4k, 8k, 16k, 32k or 64k instruction
cycles), the IDLE Timer interrupt pending bit T0PND is set,
thus generating an interrupt (if enabled), and bit 6 of the Port
G data register is reset, thus causing an exit from the IDLE
mode if the device is in that mode.
• Exit out of the Idle Mode (See Idle Mode description)
• WATCHDOG logic (See WATCHDOG description)
• Start up delay out of the HALT mode
T2C3
Bit 7
LPEN
T0PND Timer T0 Interrupt pending
T0EN
µWPND MICROWIRE/PLUS interrupt pending
µWEN
T1PNDB Timer T1 Interrupt Pending Flag for T1B capture
T1ENB Timer T1 Interrupt Enable for T1B Input capture
T2C3
T2C2
T2C1
T2C0
T2PNDA
T2ENA
T2PNDB
T2ENB
T2C2
L Port/M Port Interrupt Enable (Multi-Input
Wakeup/Interrupt)
Timer T0 Interrupt Enable (Bit 12 toggle)
Enable MICROWIRE/PLUS interrupt
edge
edge
Timer T2 mode control bit
Timer T2 mode control bit
Timer T2 mode control bit
Timer
modes 1 and 2, T2 Underflow Interrupt Pend-
ing Flag in timer mode 3
Timer T2 Interrupt Pending Flag (Autoreload
RA in mode 1, T2 Underflow in mode 2, T2A
capture edge in mode 3)
Timer T2 Interrupt Enable for Timer Underflow
or T2A Input capture edge
Timer T2 Interrupt Pending Flag for T2B cap-
ture edge
Timer T2 Interrupt Enable for Timer Underflow
or T2B Input capture edge
T2C1
T2C0
T2
T2PNDA
Start/Stop
(Continued)
c
. The user cannot read or
T2ENA
control
T2PNDB
in
T2ENB
timer
Bit 0
15
In order for an interrupt to be generated, the IDLE Timer in-
terrupt enable bit T0EN must be set, and the GIE (Global In-
terrupt Enable) bit must also be set. The T0PND flag and
T0EN bit are bits 5 and 4 of the ICNTRL register, respec-
tively. The interrupt can be used for any purpose. Typically, it
is used to perform a task upon exit from the IDLE mode. For
more information on the IDLE mode, refer to the Power Save
Modes section.
The Idle Timer period is selected by bits 0–2 of the ITMR
register Bits 3–7 of the ITMR Register are reserved and
should not be used as software flags.
ITMR Register (Address X’0xCF)
The ITMR register is cleared on Reset and the Idle Timer pe-
riod is reset to 4,096 instruction cycles.
Any time the IDLE Timer period is changed there is the pos-
sibility of generating a spurious IDLE Timer interrupt by set-
ting the T0PND bit. The user is advised to disable IDLE
Timer interrupts prior to changing the value of the ITSEL bits
of the ITMR Register and then clear the T0PND bit before at-
tempting to synchronize operation to the IDLE Timer.
TIMER T1 and TIMER T2
The device has a set of three powerful timer/counter blocks,
T1 and T2. The associated features and functioning of a
timer block are described by referring to the timer block Tx.
Since the three timer blocks, T1 and T2 are identical, all
comments are equally applicable to either of the three timer
blocks.
Each timer block consists of a 16-bit timer, Tx, and two sup-
porting 16-bit autoreload/capture registers, RxA and RxB.
Each timer block has two pins associated with it, TxA and
FIGURE 8. Functional Block Diagram for Idle Timer T0
ITSEL2
Bit 7
0
0
0
0
1
Reserved
TABLE 2. Idle Timer Window Length
ITSEL1
X
0
0
1
1
ITSEL0
0
1
0
1
X
ITSEL2
(Instruction Cycles)
Idle Timer Period
ITSEL1
16,384
32,768
65,536
4,096
8,192
www.national.com
ITSLE0
DS012837-9
Bit 0