10
Data Sheet
FlashFlex51 MCU
SST89E52RD2/RD / SST89E54RD2/RD / SST89E58RD2/RD
SST89V52RD2/RD / SST89V54RD2/RD / SST89V58RD2/RD
©2006 Silicon Storage Technology, Inc. S71255-05-000 5/06
P3[4] I T0: External count input to Timer/Counter 0
P3[5] I T1: External count input to Timer/Counter 1
P3[6] O WR#: External Data Memory Write strobe
P3[7] O RD#: External Data Memory Read strobe
PSEN# I/O Program Store Enable: PSEN# is the Read strobe to External Program Store. When the
device is executing from Internal Program Memory, PSEN# is inactive (V
OH
). When the
device is executing code from External Program Memory, PSEN# is activated twice each
machine cycle, except when access to External Data Memory while one PSEN# activation
is skipped in each machine cycle. A forced high-to-low input transition on the PSEN# pin
while the RST input is continually held high for more than 20 machine cycles will cause the
device to enter External Host mode for programming.
RST I Reset: While the oscillator is running, a high logic state on this pin for two machine cycles
will reset the device. After a reset, if the PSEN# pin is driven by a high-to-low input transition
while the RST input pin is held high, the device will enter the External Host mode, otherwise
the device will enter the Normal operation mode.
EA# I External Access Enable: EA# must be driven to V
IL
in order to enable the device to fetch
code from the External Program Memory. EA# must be driven to V
IH
for internal program
execution. However, Security lock level 4 will disable EA#, and program execution is only
possible from internal program memory. The EA# pin can tolerate a high voltage
2
of 12V.
ALE/PROG# I/O Address Latch Enable: ALE is the output signal for latching the low byte of the address
during an access to external memory. This pin is also the programming pulse input
(PROG#) for flash programming. Normally the ALE
3
is emitted at a constant rate of 1/6 the
crystal frequency
4
and can be used for external timing and clocking. One ALE pulse is
skipped during each access to external data memory. However, if AO is set to 1, ALE is dis-
abled.
P4[3:0]
5
I/O with internal
pull-ups
Port 4: Port 4 is an 4-bit bi-directional I/O port with internal pull-ups. The port 4 output buff-
ers can drive LS TTL inputs. Port 4 pins are pulled high by the internal pull-ups when ‘1’s are
written to them and can be used as inputs in this state. As inputs, port 4 pins that are exter-
nally pulled low will source current because of the internal pull-ups.
P4[0] I/O Bit 0 of port 4
P4[1] I/O Bit 1 of port 4
P4[2] / INT3# I/O Bit 2 of port 4 / INT3# External interrupt 3 input
P4[3] / INT2# I/O Bit 3 of port 4 / INT2# External interrupt 2 input
XTAL1 I Crystal 1: Input to the inverting oscillator amplifier and input to the internal clock generator
circuits.
XTAL2 O Crystal 2: Output from the inverting oscillator amplifier
V
DD
I Power Supply
V
SS
I Ground
T2-1.0 1255
1. I = Input; O = Output
2. It is not necessary to receive a 12V programming supply voltage during flash programming.
3.ALE loading issue: When ALE pin experiences higher loading (>30pf) during the reset, the MCU may accidentally enter into modes
other than normal working mode. The solution is to add a pull-up resistor of 3-50 KΩ to V
DD
, e.g. for ALE pin.
4. For 6 clock mode, ALE is emitted at 1/3 of crystal frequency.
5. Port 4 is not present on the PDIP package.
TABLE 2-1: Pin Descriptions (Continued) (2 of 2)
Symbol Type
1
Name and Functions
