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IS80C51-24PQI Datasheet(PDF) 5 Page - Integrated Silicon Solution, Inc |
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IS80C51-24PQI Datasheet(HTML) 5 Page - Integrated Silicon Solution, Inc |
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5 / 43 page  IS80C51 IS80C31 Integrated Silicon Solution, Inc. — 1-800-379-4774 5 MC003-1D 11/19/98 ISSI® Table 1. Detailed Pin Description Symbol PDIP PLCC PQFP I/O Name and Function ALE 30 33 27 I/O Address Latch Enable: Output pulse for latching the low byte of the address during an address to the external memory. In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency, and can be used for external timing or clocking. Note that one ALE pulse is skipped during each access to external data memory. EA 31 35 29 I External Access enable: EA must be externally held low to enable the device to fetch code from external program memory locations 0000H to FFFFH. If EA is held high, the device executes from internal program memory unless the program counter contains an address greater than 0FFFH. P0.0-P0.7 39-32 43-36 37-30 I/O Port 0: Port 0 is an 8-bit open-drain, bidirectional I/O port. Port 0 pins that have 1s written to them float and can be used as high- impedance inputs. Port 0 is also the multiplexed low-order address and data bus during accesses to external program and data memory. In this application, it uses strong internal pullups when emitting 1s. P1.0-P1.7 1-8 2-9 40-44 I/O Port 1: Port 1 is an 8-bit bidirectional I/O port with internal 1-3 pullups. Port 1 pins that have 1s written to them are pulled high by the internal pullups and can be used as inputs. As inputs, Port 1 pins that are externally pulled low will source current because of the internal pullups. (See DC Characteristics: IIL). The Port 1 output buffers can sink/source four TTL inputs. Port 1 also receives the low-order address byte during ROM verification. P2.0-P2.7 21-28 24-31 18-25 I/O Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pullups. Port 2 pins that have 1s written to them are pulled high by the internal pullups and can be used as inputs. As inputs, Port 2 pins that are externally pulled low will source current because of the internal pullups. (See DC Characteristics: IIL). Port 2 emits the high order address byte during fetches from external program memory and during accesses to external data memory that used 16-bit addresses (MOVX @ DPTR). In this application, Port 2 uses strong internal pullups when emitting 1s. During accesses to external data memory that use 8-bit addresses (MOVX @ Ri [i = 0, 1]), Port 2 emits the contents of the P2 Special Function Register. Port 2 also receives the high-order bits and some control signals during ROM verification. |
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