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SINGLE
COMPONENT
SYSTEM
Pin
Designation
Number
Function
RESET 4 Input which is used to initialize the processor. Also used
during PROM programming and verification. (Active
low)
(Internal
pullup
"'"
200KO)
WR 10 Output strobe during a BUS write. (Active low)
Used as write strobe to external data memory.
ALE
11
Address Latch Enable. This signal occurs once during
each
cycle and is useful as a clock output.
9
5
EA
7
XTAL1
2
XTAL2
3
The negative edge of ALE strobes address into external
data and program memory.
Program Store Enable. This output occurs
only during a
fetch to external program memory. (Active Low)
Single step input can be used in conjunction with ALE
to
"single step" the processor through each instruction.
(Active Low)
(Internal
pullup
'"
300KOl
External Access input which forces all program memory
fetches to reference external memory. Useful for
emula-
tion and debug, and essential for testing and program
verification. (Active High) (Internal
pullup
'"
10MO
on 8048/8049, 8035L, 8039 only)
One side of crystal input for internal oscillator.
Also input
for external source.
Other
side
of
crystal/external
source input.
Unless otherwise stated
inputs
do
not
have internal
pullup
resistors.
2.3 Programming, Verifying and
Pin
Function
Erasing EPROM
XTAL 1
Clock Input
(1
to 6MHz)
The internal Program Memory of the 8748
Reset
Initialization and Address
may be erased
and
reprogrammed by the user
Latching
as explained in the
following
sections. See
also the 8748 data sheet.
Test
0 Selection
of
Program
(OV)
or
2.3.1
ProgramminglVerification
Verify
(5V)
Mode
In
brief, the programmin'g process consists
EA
Activation of Program/Verify
of: activating the program mode, applying an
Modes
address, latching the address, applying data,
BUS Address and Data Input
and applying a programming pulse. Each
Data Output During Verify
word is programmed completely before moving
P2D-1
Address Input
on to the next and is followed .by a verifica-
tion step. The
following is a list of the pins
Voo
Programming Power Supply
used for programming and a description of
their functions:
PROG Program Pulse
Input
2-16