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ST10F280 数据表(PDF) 72 Page - STMicroelectronics |
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ST10F280 数据表(HTML) 72 Page - STMicroelectronics |
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72 / 186 page ![]() ST10F280 72/186 Figure 26 : XBUS Registers Associated with the Parallel Ports 12.1 - Introduction 12.1.1 - Open Drain Mode In the ST10F280 some ports provide Open Drain Control. This make is possible to switch the output driver of a port pin from a push/pull configuration to an open drain configuration. In push/pull mode a port output driver has an upper and a lower tran- sistor, thus it can actively drive the line either to a high or a low level. In open drain mode the upper transistor is always switched off, and the output driver can only actively drive the line to a low level. When writing a ‘1’ to the port latch, the lower tran- sistor is switched off and the output enters a high-impedance state. The high level must then be provided by an external pull-up device. With this feature, it is possible to connect several port pins together to a Wired-AND configuration, sav- ing external glue logic and/or additional software overhead for enabling/disabling output signals. This feature is implemented for ports P2, P3, P4, P6, P7 and P8 (see respective sections), and is controlled through the respective Open Drain Control Registers ODPx. These registers allow the individual bit-wise selection of the open drain mode for each port line. If the respective control bit ODPx.y is ‘0’ (default after reset), the output driver is in the push/pull mode. If ODPx.y is ‘1’, the open drain configuration is selected. Note that all ODPx registers are located in the ESFR space. 15 Y 14 Y 13 Y 12 Y 11 Y 10 Y 9 Y 8 Y 7 Y 6 Y 5 Y 4 Y 3 Y 2 Y 1 Y 0 Y XP9 YYYY Y Y YY YYYYYYYY XP9SET YYYY Y Y YY YYYYYYYY XP9CLR YYYY Y Y YY YYYYYYYY XP10 YYYY Y Y YY YYYYYYYY XP10DIDIS ---- - - -- ------- Y XADCMUX 15 Y 14 Y 13 Y 12 Y 11 Y 10 Y 9 Y 8 Y 7 Y 6 Y 5 Y 4 Y 3 Y 2 Y 1 Y 0 Y XDP9 YYYY Y Y YYYYYYY YYY XP9SET YYYY Y Y YYYYYYY YYY XP9CLR 15 Y 14 Y 13 Y 12 Y 11 Y 10 Y 9 Y 8 Y 7 Y 6 Y 5 Y 4 Y 3 Y 2 Y 1 Y 0 Y XOP9 YYYY Y Y YYY YYYYYYY XOP9SET YYYY Y Y YYY YYYYYYY XOP9CLR Figure 27 : Output Drivers in Push/Pull Mode and in Open Drain Mode Pin Q Push-Pull Output Driver Q Open Drain Output Driver External Pullup Pin |
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