DS87C520_1 Datasheet, PDF (5/42 Pages) Dallas Semiconductor – EPROM/ROM High-Speed Micro

DIP
21
22
23
24
25
26
27
28
10-17
10
11
12
13
14
15
16
17
31
-
PLCC
24
25
26
27
28
29
30
31
11,
13-19
11
13
14
15
16
17
18
19
35
12
34
TQFP
18
19
20
21
22
23
24
25
5, 7-13
5
7
8
9
10
11
12
13
29
6
28
SIGNAL
NAME
P2.0 (A8)
P2.1 (A9)
P2.2(A10)
P2.3(A11)
P2.4(A12)
P2.5(A13)
P2.6(A14)
P2.7(A15)
P3.0-P3.7
EA
NC
DS87C520/DS83C520
DESCRIPTION
Port 2 (A8-15) - I/O. Port 2 is a bi-directional I/O port.
The reset condition of Port 2 is logic high. In this state, a
weak pullup holds the port high. This condition also serves
as an input mode, since any external circuit that writes to
the port will overcome the weak pullup. When software
writes a 0 to any port pin, the DS87C520/DS83C520 will
activate a strong pulldown that remains on until either a 1
is written or a reset occurs. Writing a 1 after the port has
been at 0 will cause a strong transition driver to turn on,
followed by a weaker sustaining pullup. Once the
momentary strong driver turns off, the port again becomes
both the output high and input state. As an alternate
function Port 2 can function as MSB of the external
address bus. This bus can be used to read external ROM
and read/write external RAM memory or peripherals.
Port 3 - I/O. Port 3 functions as both an 8-bit bi-
directional I/O port and an alternate functional interface
for External Interrupts, Serial Port 0, Timer 0 and 1 Inputs,
and RD and WR strobes. The reset condition of Port 3 is
with all bits at a logic 1. In this state, a weak pullup holds
the port high. This condition also serves as an input mode,
since any external circuit that writes to the port will
overcome the weak pullup. When software writes a 0 to
any port pin, the DS87C520/DS83C520 will activate a
strong pulldown that remains on until either a 1 is written
or a reset occurs. Writing a 1 after the port has been at 0
will cause a strong transition driver to turn on, followed by
a weaker sustaining pullup. Once the momentary strong
driver turns off, the port again becomes both the output
high and input state. The alternate modes of Port 3 are
outlined below.
Port Alternate Mode
P3.0 RXD0 Serial Port 0 Input
P3.1 TXD0 Serial Port 0 Output
P3.2 INT0
External Interrupt 0
P3.3 INT1
P3.4 T0
P3.5 T1
External Interrupt 1
Timer 0 External Input
Timer 1 External Input
P3.6 WR
External Data Memory Write Strobe
P3.7 RD
External Data Memory Read Strobe
EA - Input. Connect to ground to force the
DS87C520/DS83C520 to use an external ROM. The
internal RAM is still accessible as determined by register
settings. Connect EA to V_CC to use internal ROM.
NC - Reserved. These pins should not be connected. They
are reserved for use with future devices in this family.
5 of 42