AT89S8252-16AA ATMEL Corporation, AT89S8252-16AA Datasheet - Page 14

• Manufacturer Part Number: AT89S8252-16AA
• Description: 8-Bit Microcontroller with 8K Bytes Flash
• Manufacturer: ATMEL Corporation

Programmable Clock Out
A 50% duty cycle clock can be programmed to come out on
P1.0, as shown in Figure 5. This pin, besides being a regu-
lar I/0 pin, has two alternate functions. It can be pro-
grammed to input the external clock for Timer/Counter 2 or
to output a 50% duty cycle clock ranging from 61 Hz to 4
MHz at a 16 MHz operating frequency.
To configure the Timer/Counter 2 as a clock generator, bit
C/T2 (T2CON.1) must be cleared and bit T2OE (T2MOD.1)
must be set. Bit TR2 (T2CON.2) starts and stops the timer.
The clock-out frequency depends on the oscillator fre-
quency and the reload value of Timer 2 capture registers
(RCAP2H, RCAP2L), as shown in the following equation.
In the clock-out mode, Timer 2 rollovers will not generate
an interrupt. This behavior is similar to when Timer 2 is
used as a baud-rate generator. It is possible to use Timer 2
as a baud-rate generator and a clock generator simulta-
neously. Note, however, that the baud-rate and clock-out
frequencies cannot be determined independently from one
another since they both use RCAP2H and RCAP2L.
Figure 6. SPI Block Diagram
4-118
Clock Out Frequency
=
AT89S8252
SPI STATUS REGISTER
OSCILLATOR
÷4÷16÷64÷128
------------------------------------------------------------------------------------------ -
4
SELECT
DIVIDER
SPI CONTROL
65536
Oscillator Frequency
–
SPI INTERRUPT
RCAP2H,RCAP2L
SPI CLOCK (MASTER)
REQUEST
MSTR
SPE
8
INTERNAL
MSB
DATA BUS
8/16-BIT SHIFT REGISTER
8
READ DATA BUFFER
8
SPI CONTROL REGISTER
UART
The UART in the AT89S8252 operates the same way as
the UART in the AT89C51, AT89C52 and AT89C55. For
further information, see the October 1995 Microcontroller
Data Book, page 2-49, section titled, “Serial Interface.”
Serial Peripheral Interface
The serial peripheral interface (SPI) allows high-speed syn-
chronous data transfer between the AT89S8252 and
peripheral devices or between several AT89S8252
devices. The AT89S8252 SPI features include the follow-
ing:
• Full-Duplex, 3-Wire Synchronous Data Transfer
• Master or Slave Operation
• 1.5-MHz Bit Frequency (max.)
• LSB First or MSB First Data Transfer
• Four Programmable Bit Rates
• End of Transmission Interrupt Flag
• Write Collision Flag Protection
• Wakeup from Idle Mode (Slave Mode Only)
CLOCK
LOGIC
LSB
CLOCK
S
M
M
S
S
M
MISO
MOSI
P1.6
P1.5
SCK
P1.4
1.7
SS