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Q67126-C2001 Datasheet(PDF) 10 Page - Siemens Semiconductor Group |
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Q67126-C2001 Datasheet(HTML) 10 Page - Siemens Semiconductor Group |
10 / 65 page Semiconductor Group 10 1997-10-01 C540U C541U P2.0 - P2.7 24 - 31 28 - 35 I/O Port 2 is an 8-bit quasi-bidirectional I/O port with internal pullup resistors. Port 2 pins that have 1's written to them are pulled high by the internal pullup resistors, and in that state can be used as inputs. As inputs, port 2 pins being externally pulled low will source current (I IL, in the DC characteristics) because of the internal pullup resistors. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that use 16-bit addresses (MOVX @DPTR). In this application it uses strong internal pullup resistors when issuing 1's. During accesses to external data memory that use 8-bit addresses (MOVX @Ri), port 2 issues the contents of the P2 special function register. PSEN 32 38 O The Program Store Enable output is a control signal that enables the external program memory to the bus during external fetch operations. It is activated every six oscillator periods except during external data memory accesses. The signal remains high during internal program execution. ALE 33 39 O The Address Latch enable output is used for latching the address into external memory during normal operation. It is activated every six oscillator periods except during an external data memory access. EA 35 42 I External Access Enable When held high, the C540U/C541U executes instructions from the internal ROM as long as the PC is less than 1000H for the C540U or less than 2000H for the C541U. When held low, the C540U/ C541U fetches all instructions from external program memory. For the C540U-L/C541U-L this pin must be tied low. *) I = Input O = Output Table 2 Pin Definitions and Functions (cont’d) Symbol Pin Numbers I/O*) Function P-LCC-44 P-SDIP-52 |
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