DS12887A Datasheet, PDF (3/19 Pages) Maxim Integrated Products – Real-Time Clock

DS5000(T)
PIN DESCRIPTION
PIN NUMBER
DESCRIPTION
1–8
P1.0 – P1.7. General purpose I/O Port 1.
9
RST – Active high reset input. A logic 1 applied to this pin will activate a reset state. This pin
is pulled down internally so this pin can be left unconnected if not used.
10
P3.0 RXD. General purpose I/O port pin 3.0. Also serves as the receive signal for the on
board UART. This pin should not be connected directly to a PC COM port.
11
P3.1 TXD. General purpose I/O port pin 3.1. Also serves as the transmit signal for the on
board UART. This pin should not be connected directly to a PC COM port.
12
P3.2 INT0. General purpose I/O port pin 3.2. Also serves as the active low External
Interrupt 0.
13
P3.3 INT1. General purpose I/O port pin 3.3. Also serves as the active low External
Interrupt 1.
14
P3.4 T0. General purpose I/O port pin 3.4. Also serves as the Timer 0 input.
15
P3.5 T1. General purpose I/O port pin 3.5. Also serves as the Timer 1 input.
16
P3.6 WR. General purpose I/O port pin. Also serves as the write strobe for Expanded
bus operation.
17
P3.7 RD. General purpose I/O port pin. Also serves as the read strobe for Expanded bus
operation.
18, 19
XTAL2, XTAL1. Used to connect an external crystal to the internal oscillator. XTAL1 is the
input to an inverting amplifier and XTAL2 is the output.
20
21–28
GND. Logic ground.
P2.0–P2.7. General purpose I/O Port 2. Also serves as the MSB of the Expanded Address
bus.
29
PSEN – Program Store Enable. This active low signal is used to enable an external program
memory when using the Expanded bus. It is normally an output and should be unconnected
if not used. PSEN also is used to invoke the Bootstrap Loader. At this time, PSEN will be
pulled down externally. This should only be done once the DS5000(T) is already in a reset
state. The device that pulls down should be open drain since it must not interfere with PSEN
under normal operation.
30
ALE – Address Latch Enable. Used to de–multiplex the multiplexed Expanded Address/Data
bus on Port 0. This pin is normally connected to the clock input on a ’373 type transparent
latch. When using a parallel programmer, this pin also assumes the PROG function for pro-
gramming pulses.
31
EA – External Access. This pin forces the DS5000(T) to behave like an 8031. No internal
memory (or clock) will be available when this pin is at a logic low. Since this pin is pulled down
internally, it should be connected to +5V to use NV RAM. In a parallel programmer, this pin
also serves as V_PP for super voltage pulses.
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