ST10F280 datasheet(87/186 Pages) STMICROELECTRONICS

87 / 186 page

ST10F280

87/186

Pin P3.12 (BHE/WRH) is another pin with an alternate output function, however, its structure is slightly dif-

ferent (see figure Figure 37). After reset the BHE or WRH function must be used depending on the sys-

tem start-up configuration. In either of these cases, there is no possibility to program any port latches

before. Thus, the appropriate alternate function is selected automatically. If BHE/WRH is not used in the

system, this pin can be used for general purpose I/O by disabling the alternate function (BYTDIS = ‘1’ /

WRCFG=’0’).

Note: Enabling the BHE or WRH function automatically enables the P3.12 output driver. Setting bit

DP3.12=’1’ is not required.

During bus hold, pin P3.12 is switched back to its standard function and is then controlled by

DP3.12 and P3.12. Keep DP3.12 = ’0’ in this case to ensure floating in hold mode.

12.6 - Port 4

If this 8-bit port is used for general purpose I/O, the direction of each line can be configured via the corre-

sponding direction register DP4.

P4 (FFC8h / E4h)

SFR

Reset Value: - - 00h

Figure 37 : Block Diagram of Pins P3.15 (CLKOUT) and P3.12 (BHE/WRH)

9876543210

--------

P4.7

P4.6

P4.5

P4.4

P4.3

P4.2

P4.1

P4.0

Bit

Function

P4.y

Port data register P4 bit y

Direction

Latch

Write DP3.x

Read DP3.x

Port Output

Latch

Write P3.x

Read P3.x

MUX

Alternate

Data

Output

MUX

“1”

Input

Latch

P3.12/BHE

P3.15/CLKOUT

Output

Buffer

x = 15, 12

Alternate

Function

Enable

CPU Clock

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