P51XAG30KFA PHILIPS [NXP Semiconductors], P51XAG30KFA Datasheet - Page 20
Manufacturer Part Number
XA 16-bit microcontroller family 32K/512 OTP/ROM/ROMless, watchdog, 2 UARTs
PHILIPS [NXP Semiconductors]
I/O PORT OUTPUT CONFIGURATION
Each I/O port pin can be user configured to one of 4 output types.
The types are Quasi-bidirectional (essentially the same as standard
80C51 family I/O ports), Open-Drain, Push-Pull, and Off (high
impedance). The default configuration after reset is
Quasi-bidirectional. However, in the ROMless mode (the EA pin is
low at reset), the port pins that comprise the external data bus will
default to push-pull outputs.
I/O port output configurations are determined by the settings in port
configuration SFRs. There are 2 SFRs for each port, called
PnCFGA and PnCFGB, where “n” is the port number. One bit in
each of the 2 SFRs relates to the output setting for the
corresponding port pin, allowing any combination of the 2 output
types to be mixed on those port pins. For instance, the output type
of port 1 pin 3 is controlled by the setting of bit 3 in the SFRs
P1CFGA and P1CFGB.
Table 4 shows the configuration register settings for the 4 port
output types. The electrical characteristics of each output type may
be found in the DC Characteristic table.
Table 4. Port Configuration Register Settings
Mode changes may cause glitches to occur during transitions. When
modifying both registers, WRITE instructions should be carried out
The external program/data bus allows for 8-bit or 16-bit bus width,
and address sizes from 12 to 20 bits. The bus width is selected by
an input at reset (see Reset Options below), while the address size
is set by the program in a configuration register. If all off-chip code is
selected (through the use of the EA pin), the initial code fetches will
be done with the maximum address size (20 bits).
The device is reset whenever a logic “0“ is applied to RST for at
least 10 microseconds, placing a low level on the pin re-initializes
the on-chip logic. Reset must be asserted when power is initially
applied to the XA and held until the oscillator is running.
The duration of reset must be extended when power is initially
applied or when using reset to exit power down mode. This is due to
the need to allow the oscillator time to start up and stabilize. For
most power supply ramp up conditions, this time is 10 milliseconds.
1999 Apr 07
XA 16-bit microcontroller family
32K/512 OTP/ROM/ROMless, watchdog, 2 UARTs
Off (high impedance)
Port Output Mode
As it is brought high again, an exception is generated which causes
the processor to jump to the address contained in the memory
location 0000. The destination of the reset jump must be located in
the first 64k of code address on power-up, all vectors are 16-bit
values and so point to page zero addresses only. After a reset the
RAM contents are indeterminate.
The EA pin is sampled on the rising edge of the RST pulse, and
determines whether the device is to begin execution from internal or
external code memory. EA pulled high configures the XA in
single-chip mode. If EA is driven low, the device enters ROMless
mode. After Reset is released, the EA/WAIT pin becomes a bus wait
signal for external bus transactions.
The BUSW/P3.5 pin is weakly pulled high while reset is asserted,
allowing simple biasing of the pin with a resistor to ground to select
the alternate bus width. If the BUSW pin is not driven at reset, the
weak pullup will cause a 1 to be loaded for the bus width, giving a
16-bit external bus. BUSW may be pulled low with a 2.7K or smaller
value resistor, giving an 8-bit external bus. The bus width setting
from the BUSW pin may be overridden by software once the user
program is running.
Both EA and BUSW must be held for three oscillator clock times
after reset is deasserted to guarantee that their values are latched
POWER REDUCTION MODES
The XA-G3 supports Idle and Power Down modes of power
reduction. The idle mode leaves some peripherals running to allow
them to wake up the processor when an interrupt is generated. The
power down mode stops the oscillator in order to minimize power.
The processor can be made to exit power down mode via reset or
one of the external interrupt inputs. In order to use an external
interrupt to re-activate the XA while in power down mode, the
external interrupt must be enabled and be configured to level
sensitive mode. In power down mode, the power supply voltage may
be reduced to the RAM keep-alive voltage (2V), retaining the RAM,
register, and SFR values at the point where the power down mode
SOME TYPICAL VALUES FOR R AND C:
(ASSUMING THAT THE V
R = 100K, C = 1.0 F
R = 1.0M, C = 0.1 F
Figure 15. Recommended Reset Circuit
RISE TIME IS 1ms OR LESS)