Siemens EF 88H Series Manual de usuario descargar pdf (Pagina 40)

Semiconductor Group 6-6

On-Chip Peripheral Components

C501

Port 0, in contrast to ports 1, 2 and 3, is considered as “true” bidirectional, because the port 0 pins

float when configured as inputs. Thus, this port differs in not having internal pullups. The pullup FET

in the P0 output driver (see figure 6-7) is used only when the port is emitting 1 s during the external

memory accesses. Otherwise, the pullup is always off. Consequently, P0 lines that are used as

output port lines are open drain lines. Writing a “1” to the port latch leaves both output FETs off and

the pin floats. In that condition it can be used as high-impedance input. If port 0 is configured as

general I/O port and has to emit logic high-level (1), external pullups are required.

Figure 6-7

Port 0 Circuitry

MCS02122

CLK

Bit

Latch

Control

Addr./Data

MUX

Read

Latch

Read

Write

Int. Bus

Port

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Siemens EF 88H Series Manual de usuario Pagina 40