AT89LP828 Atmel Corporation, AT89LP828 Datasheet - Page 23

• Manufacturer Part Number: AT89LP828
• Manufacturer: Atmel Corporation

Specifications of AT89LP828

• Flash (kbytes): 8 Kbytes
• Max. Operating Frequency: 25 MHz
• Cpu: 8051-1C
• Max I/o Pins: 30
• Spi: 1
• Uart: 1
• Sram (kbytes): 0.75
• Eeprom (bytes): 1024
• Self Program Memory: IAP
• Operating Voltage (vcc): 2.4 to 5.5
• Timers: 3
• Isp: SPI/OCD
• Watchdog: Yes

Table 6-2.
7. Reset
7.1
3654A–MICRO–8/09
TPS [3 - 0]
CDV [2 - 0]
COE
Symbol
CLKREG = 8FH
Not Bit Addressable
Bit
Power-on Reset
CLKREG
Function
Timer Prescaler. The Timer Prescaler selects the time base for Timer 0, Timer 1, Timer 2 and the Watchdog Timer.
The prescaler is implemented as a 4-bit binary down counter. When the counter reaches zero it is reloaded with the
value stored in the TPS bits to give a division ratio between 1 and 16. By default the timers will count every clock
cycle (TPS = 0000B). To configure the timers to count at a standard 8051 rate of once every 12 clock cycles, TPS
should be set to 1011B.
System Clock Division. Determines the frequency of the system clock relative to the oscillator clock source.
Clock Out Enable. Set COE to output the system clock divided by 2 on XTAL2 (P4.1). The internal RC oscillator or
external clock source must be selected in order to use this feature and P4.1 must be configured as an output.
CDIV2
TPS3
0
0
0
0
1
1
1
1
7
– Clock Control Register
CDIV1
During reset, all I/O Registers are set to their initial values, the port pins are tristated, and the
program starts execution from the Reset Vector, 0000H. The AT89LP428/828 has five sources
of reset: power-on reset, brown-out reset, external reset, watchdog reset, and software reset.
A Power-on Reset (POR) is generated by an on-chip detection circuit. The detection level V
is nominally 1.4V. The POR is activated whenever V
cuit can be used to trigger the start-up reset or to detect a supply voltage failure in devices
without a brown-out detector. The POR circuit ensures that the device is reset from power-on. A
power-on sequence is shown in
threshold voltage V
sequence completes, the start-up timer determines how long the device is kept in POR after V
rise. The POR signal is activated again, without any delay, when V
threshold level. A Power-on Reset (i.e. a cold reset) will set the POF flag in PCON. The internally
generated reset can be extended beyond the power-on period by holding the RST pin low longer
than the time-out.
0
0
1
1
0
0
1
1
TPS2
6
CDIV0
0
1
0
1
0
1
0
1
TPS1
5
System Clock Frequency
f
f
f
f
f
f
reserved
reserved
OSC
OSC
OSC
OSC
OSC
OSC
POR
/1
/2
/4
/8
/16
/32
, an initialization sequence lasting t
TPS0
4
Figure 7-1 on page
CDV2
3
CC
24. When V
CDV1
is below the detection level. The POR cir-
2
POR
is started. When the initialization
CC
Reset Value = 0000 0000B
AT89LP428/828
reaches the Power-on Reset
CDV0
1
CC
falls below the POR
COE
0
POR
23
CC