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ST62E25BD6 Datasheet(PDF) 38 Page - STMicroelectronics |
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ST62E25BD6 Datasheet(HTML) 38 Page - STMicroelectronics |
38 / 105 page ST6215C ST6225C 38/105 8 I/O PORTS 8.1 INTRODUCTION Each I/O port contains up to 8 pins. Each pin can be programmed independently as digital input (with or without pull-up and interrupt generation), digital output (open drain, push-pull) or analog in- put (when available). The I/O pins can be used in either standard or al- ternate function mode. Standard I/O mode is used for: – Transfer of data through digital inputs and out- puts (on specific pins): – External interrupt generation Alternate function mode is used for: – Alternate signal input/output for the on-chip peripherals The generic I/O block diagram is shown in Figure 23. 8.2 FUNCTIONAL DESCRIPTION Each port is associated with 3 registers located in Data space: – Data Register (DR) – Data Direction Register (DDR) – Option Register (OR) Each I/O pin may be programmed using the corre- sponding register bits in the DDR, DR and OR reg- isters: bit x corresponding to pin x of the port. Table 8 illustrates the various port configurations which can be selected by user software. During MCU initialization, all I/O registers are cleared and the input mode with pull-up and no in- terrupt generation is selected for all the pins, thus avoiding pin conflicts. 8.2.1 Digital Input Modes The input configuration is selected by clearing the corresponding DDR register bit. In this case, reading the DR register returns the digital value applied to the external I/O pin. Different input modes can be selected by software through the DR and OR registers, see Table 8. External Interrupt Function All input lines can be individually connected by software to the interrupt system by programming the OR and DR registers accordingly. The inter- rupt trigger modes (falling edge, rising edge and low level) can be configured by software for each port as described in the Interrupt section. 8.2.2 Analog Inputs Some pins can be configured as analog inputs by programming the OR and DR registers according- ly, see Table 8. These analog inputs are connect- ed to the on-chip 8-bit Analog to Digital Converter. Caution: ONLY ONE pin should be programmed as an analog input at any time, since by selecting more than one input simultaneously their pins will be effectively shorted. 8.2.3 Output Modes The output configuration is selected by setting the corresponding DDR register bit. In this case, writ- ing to the DR register applies this digital value to the I/O pin through the latch. Then, reading the DR register returns the previously stored value. Two different output modes can be selected by software through the OR register: push-pull and open-drain. DR register value and output pin status: Note: The open drain setting is not a true open drain. This means it has the same structure as the push-pull setting but the P-buffer is deactivated. To avoid damaging the device, please respect the VOUT absolute maximum rating described in the Electrical Characteristics section. 8.2.4 Alternate Functions When an on-chip peripheral is configured to use a pin, the alternate function (timer input/output...) is not systematically selected but has to be config- ured through the DDR, OR and DR registers. Re- fer to the chapter describing the peripheral for more details. DR Push-pull Open-drain 0VSS VSS 1VDD Floating 1 |
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