SDA5252 SIEMENS [Siemens Semiconductor Group], SDA5252 Datasheet - Page 78

• Manufacturer Part Number: SDA5252
• Description: TVTEXT 8-Bit Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

Semiconductor Group
unintentionally entering the power-down mode. The following instruction sequence may
serve as an example:
ORL
ORL
The instruction that sets bit PDS is the last instruction executed before going into power-
down mode.
If idle mode and power-down mode are invoked simultaneously, the power-down mode
takes precedence.
The only exit from power-down mode is a hardware reset. The reset will redefine all
SFRs, but will not change the contents of internal RAM.
6.3.6
There are 26 I/O-pins configured as three 8-bit ports, one 4-bit-port (P2.0 – 2.3) and one
2-bit port (P4.0 – 4.1, P4.1 for ROM-less version only). Each pin can be individually and
independently programmed as input or output and each can be configured dynamically.
An instruction that uses a port's bit/byte as a source operand reads a value that is the
logical AND of the last value written to the bit/byte and the polarity being applied to the
pin/pins by an external device (this assumes that none of the processor's electrical
specifications are being violated). An instruction that reads a bit/byte, operates on the
content, and writes the result back to the bit/byte, reads the last value written to the
bit/byte instead of the logic level at the pin/pins. Pins comprising a single port can be
made a mixed collection of inputs and outputs by writing a “one” to each pin that is to be
an input. Each time an instruction uses a port as the destination, the operation must write
“ones” to those bits that correspond to the input pins. An input to a port pin needs not to
be synchronized to the oscillator.
All the port latches have “one” s written to them by the reset function. If a “zero” is
subsequently written to a port latch, it can be reconfigured as an input by writing a “one”
to it.
The instructions that perform a read of, operation on, and write to a port's bit/byte are
INC, DEC, CPL, JBC, SETB, CLR, MOV P.X, CJNE, DJNZ, ANL, ORL, and XRL. The
source read by these operations is the last value that was written to the port, without
regard to the levels being applied at the pins. This insures that bits written to a “one” (for
use as inputs) are not inadvertently cleared.
Port 0 has an open-drain output. Writing a “one” to the bit latch leaves the output
transistor off, so the pin floats.
In that condition it can be used as a high-impedance input. Port 0 is considered “true
bidirectional”, because when configured as an input it floats.
Ports 1, 3 and 4 have “quasi-bidirectional” output drivers which comprise an internal
pullup resistor of 10 k
Ports and I/O-Pins
PCON,#00000010
PCON,#01000000
to 40 k . When configured as inputs they pull high and will
B
B
Set bit PDE, bit PDS must not be set.
Set bit PDS, bit PDE must not be set.
78
SDA 525x
1998-04-08