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DS83C520-MNL Datasheet(PDF) 4 Page - Dallas Semiconductor |
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DS83C520-MNL Datasheet(HTML) 4 Page - Dallas Semiconductor |
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4 / 44 page  DS87C520/DS83C520 EPROM/ROM High-Speed Microcontrollers 4 of 44 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) |
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