Datasheet

DS87C520/DS83C520 EPROM/ROM High-Speed Microcontrollers
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PIN DESCRIPTION (continued)
PIN
DIP PLCC TQFP
NAME FUNCTION
30 33 27 ALE
Address Latch Enable Output. The ALE functions as a clock to
latch the external address LSB from the multiplexed address/data bus
on Port 0. This signal is commonly connected to the latch enable of an
external 373 family transparent latch. ALE has a pulse width of 1.5
XTAL1 cycles and a period of four XTAL1 cycles. ALE is forced
high when the DS87C520/DS83C520 are in a reset condition. ALE
can also be disabled and forced high by writing ALEOFF = 1
(PMR.2). ALE operates independently of ALEOFF during external
memory accesses.
39 43 37 P0.0 (AD0)
38 42 36 P0.1 (AD1)
37 41 35 P0.2 (AD2)
36 40 34 P0.3 (AD3)
35 39 33 P0.4 (AD4)
34 38 32 P0.5 (AD5)
33 37 31 P0.6 (AD6)
32 36 30 P0.7 (AD7)
Port 0 (AD0–7), I/O. Port 0 is an open-drain, 8-bit, bidirectional I/O
port. As an alternate function Port 0 can function as the multiplexed
address/data bus to access off-chip memory. During the time when
ALE is high, the LSB of a memory address is presented. When ALE
falls to a logic 0, the port transitions to a bidirectional data bus. This
bus is used to read external ROM and read/write external RAM
memory or peripherals. When used as a memory bus, the port
provides active high drivers. The reset condition of Port 0 is tri-state.
Pullup resistors are required when using Port 0 as an I/O port.
1 2 40 P1.0
2 3 41 P1.1
3 4 42 P1.2
4 5 43 P1.3
5 6 44 P1.4
6 7 1 P1.5
7 8 2 P1.6
8 9 3 P1.7
Port 1, I/O. Port 1 functions as both an 8-bit, bidirectional I/O port
and an alternate functional interface for Timer 2 I/O, new External
Interrupts, and new Serial Port 1. The reset condition of Port 1 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 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 the output high (and input) state. The alternate
modes of Port 1 are out-lines as follows.
Port Alternate Function
P1.0 T2 External I/O for Timer/Counter 2
P1.1 T2EX EX Timer/Counter 2 Capture/Reload Trigger
P1.2 RXD1 Serial Port 1 Input
P1.3 TXD1 Serial Port 1 Output
P1.4 INT2 External Interrupt 2 (Positive Edge Detect)
P1.5 INT3 External Interrupt 3 (Negative Edge Detect)
P1.6 INT4 External Interrupt 4 (Positive Edge Detect)
P1.7 INT5 External Interrupt 5 (Negative Edge Detect)