3.13
EA/VPP
External Access Enable. EA must be strapped to GND in order to enable the device to fetch
code from external program memory locations starting at 0000H up to FFFFH. Note, however,
that if lock bit 1 is programmed, EA will be internally latched on reset.
EA should be strapped to V
CC
for internal program executions. This pin also receives the 12-volt
programming enable voltage (V
PP
) during Flash programming when 12-volt programming is
selected.
3.14
XTAL1
Input to the inverting oscillator amplifier and input to the internal clock operating circuit.
3.15
XTAL2
Output from the inverting oscillator amplifier.
4. Block Diagram
P0.0 - P0.7
P2.0 - P2.7
V
CC
PORT 0 DRIVERS
GND
PORT 2 DRIVERS
EEPROM
RAM ADDR.
REGISTER
RAM
PORT 0
LATCH
PORT 2
LATCH
FLASH
B
REGISTER
ACC
STACK
POINTER
PROGRAM
ADDRESS
REGISTER
BUFFER
TMP2
TMP1
ALU
INTERRUPT, SERIAL PORT,
AND TIMER BLOCKS
PC
INCREMENTER
PSW
PROGRAM
COUNTER
PSEN
ALE/PROG
EA / V
PP
RST
WATCH
DOG
PORT 3
LATCH
TIMING
AND
CONTROL
INSTRUCTION
REGISTER
DUAL
DPTR
PORT 1
LATCH
SPI
PORT
PROGRAM
LOGIC
OSC
PORT 3 DRIVERS
PORT 1 DRIVERS
P3.0 - P3.7
P1.0 - P1.7
6
AT89S8253
3286H–MICRO–9/05
ATMEL [ ATMEL CORPORATION ]
