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UM0404
Dedicated pins
7 Dedicated
pins
Most of the input/output or control signals of the ST10F276 are realized as alternate
functions of pins of the parallel ports. There is, however, a number of signals that use
separate pins, including the oscillator, special control signals and the power supply.
The
summarizes the dedicated pins of the ST10F276.
Table 29. Summary of dedicated pins
Pin(s)
Function
ALE
Address Latch Enable:
controls external address latches that provide a stable address in
multiplexed bus modes. ALE is activated for every external bus cycle independent of the
selected bus mode. It is also activated for bus cycles with a de-multiplexed address bus. When
an external bus is enabled (if one or more of the BUSACT bit is set) also X-Peripheral
accesses will generate an active ALE signal.
ALE is not activated for internal accesses, like accesses to IFlash, to the IRAM and to the
special function registers. In single chip mode, when no external bus is enabled (no BUSACT
bit set), ALE will also remain inactive for X-Peripheral accesses. During reset, during Hold
mode and during Adapt mode an internal pull-down ensures an inactive (low) level on the ALE
output.
RD
External Read Strobe:
controls the output drivers of external memory or peripherals when the
ST10F276 reads data from these external devices. During reset, during Hold mode and during
Adapt mode an internal pull-up ensures an inactive high level on the RD output.
WR/WRL
External Write/Write Low Strobe:
controls the data transfer from the ST10F276 to an external
memory or peripheral device. This pin may either provide a general WR signal activated for
both byte and word write accesses, or specifically control the low byte of an external 16-bit
device (WRL) together with the signal WRH (alternate function of P3.12/BHE). During reset,
during Hold mode and during Adapt mode an internal pull-up ensures an inactive (high) level
on the WR/WRL output.
READY/READY
Ready Input:
receives a control signal from an external memory or peripheral device that is
used to terminate an external bus cycle, provided that this function is enabled for the current
bus cycle. READY/READY may be used as synchronous READY/READY or may be evaluated
asynchronously. The polarity can be set to READY or READY by setting bit 13 in the BUSCON
register.
EA / V
STBY
External Access Enable:
determines, if the ST10F276 after reset starts fetching code from
the internal Memory area (EA
=
‘1’) or via the external bus interface (EA
=
‘0’).
This pin is also used (when Stand-by mode is entered, that is ST10F276 under reset and main
V
DD
turned off) to bias the 32 kHz oscillator amplifier circuit and to provide a reference voltage
for the low-power embedded voltage regulator, which generates the internal 1.8V supply for the
RTC module (when not disabled) and to retain data inside the Stand-by portion of the XRAM
(16 Kbyte).
It can range from 4.5 to 5.5V (6V for a reduced amount of time during the device life, 4.0V
when RTC and 32 kHz on-chip oscillator amplifier are turned off). In running mode, this pin can
be tied low during reset without affecting 32 kHz oscillator, RTC and XRAM activities, since the
presence of a stable V
DD
guarantees the proper biasing of all those modules.
NMI
Non-Maskable Interrupt Input:
allows to trigger a high priority trap via an external signal. It
can be used as power fail input or to validate the PWRDN instruction that switches the
ST10F276 into Power Down mode.