Preliminary C8051F120/1/2/3 C8051F124/5/6/7 - KEMT FEI TUKE

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C8051F120/1/2/3 C8051F124/5/6/7 Preliminary 18.2.3. Configuring Port Pins as Digital Inputs A Port pin is configured as a digital input by setting its output mode to “Open-Drain” and writing a logic 1 to the associated bit in the Port Data register. For example, P7.7 is configured as a digital input by setting P7MDOUT.7 to a logic0andP7.7toalogic1. 18.2.4. Weak Pull-ups By default, each Port pin has an internal weak pull-up device enabled which provides a resistive connection (about 100 kΩ) between the pin and VDD. The weak pull-up devices can be globally disabled by writing a logic 1 to the Weak Pull-up Disable bit, (WEAKPUD, XBR2.7). The weak pull-up is automatically deactivated on any pin that is driving a logic 0; that is, an output pin will not contend with its own pull-up device. 18.2.5. External Memory Interface If the External Memory Interface (EMIF) is enabled on the High ports (Ports 4 through 7), EMIFLE (XBR2.5) should be set to a logic 0. If the External Memory Interface is enabled on the High ports and an off-chip MOVX operation occurs, the External Memory Interface will control the output states of the affected Port pins during the execution phase of the MOVX instruction, regardless of the settings of the Port Data registers. The output configuration of the Port pins is not affected by the EMIF operation, except that Read operations will explicitly disable the output drivers on the Data Bus during the MOVX execution. See Section “17. EXTERNAL DATA MEMORY INTERFACE AND ON-CHIP XRAM” on page 187 for more information about the External Memory Interface. Page 220 DS008-0.8-AUG02 © 2002 Cygnal Integrated Products, Inc.
Preliminary C8051F120/1/2/3 C8051F124/5/6/7 Figure 18.19. P4: Port4 Data Register R/W R/W R/W R/W R/W R/W R/W R/W Reset Value P4.7 P4.6 P4.5 P4.4 P4.3 P4.2 P4.1 P4.0 11111111 Bit Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 Addressable SFR Address: 0xC8 SFR Page: F Bits7-0: P4.[7:0]: Port4 Output Latch Bits. Write - Output appears on I/O pins. 0: Logic Low Output. 1: Logic High Output (Open-Drain if corresponding P4MDOUT.n bit = 0). See Figure 18.20. Read - Returns states of I/O pins. 0: P4.n pin is logic low. 1: P4.n pin is logic high. Note: P4.7 (/WR), P4.6 (/RD), and P4.5 (ALE) can be driven by the External Data Memory Interface. See Section “17. EXTERNAL DATA MEMORY INTERFACE AND ON-CHIP XRAM” on page 187 for more information. Figure 18.20. P4MDOUT: Port4 Output Mode Register R/W R/W R/W R/W R/W R/W R/W R/W Reset Value 00000000 Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 SFR Address: 0x9C SFR Page: F Bits7-0: P4MDOUT.[7:0]: Port4 Output Mode Bits. 0: Port Pin output mode is configured as Open-Drain. 1: Port Pin output mode is configured as Push-Pull. © 2002 Cygnal Integrated Products, Inc. DS008-0.8-AUG02 Page 221
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Preliminary C8051F120/1/2/3 C8051F124/5/6/7 - KEMT FEI TUKE

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