ST10F280 datasheet(72/186 Pages) STMICROELECTRONICS

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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.

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

XDP9

YYYY Y Y YYYYYYY YYY

XP9SET

YYYY Y Y YYYYYYY YYY

XP9CLR

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

Push-Pull Output Driver

Open Drain Output Driver

External

Pullup

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