
C165H
Dedicated Pins
Data Sheet
164
2001-04-19
PRELMNARY
oscillation allowance of the oscillator circuitry.
An external clock signal may be fed to the input XTAL1, leaving XTAL2 open.
Note:
It is strongly recommended to measure the oscillation allowance (or margin) in the
final target system (layout) to determine the optimum parameters for the oscillator
operation.
-EXCERPT-
External Write Strobe WR/WRL
controls the data transfer from the C165H to an
external memory or peripheral device. This pin may either provide an 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 and during Hold mode an internal pullup ensures an inactive (high)
level on the WR/WRL output.
Note:
Whether
RD
and
WR/WRL
remain idle during X-peripheral accesses depends on
the value of bit VISIBLE of register SYSCON.
Ready Input READY
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 may be used as synchronous READY or may
be evaluated asynchronously. When waitstates are defined for a READY controlled
address window the READY input is not evaluated during these waitstates.
External Access Enable Pin EA
is dedicated for on-chip ROM derivates. In this case it
determines, if the chip after reset starts fetching code from the internal ROM area
(EA=’1’) or via the external bus interface (EA=’0’).
For the ROM-less C165H be sure to
hold this input low.
Non-Maskable Interrupt Input NMI
allows to trigger a high priority trap via an external
signal (eg. a power-fail signal). It also serves to validate the PWRDN instruction that
switches the C165H into Power-Down mode. The NMI pin is sampled with every CPU
clock cycle to detect transitions.
Oscillator Input XTAL1 and Output XTAL2
connect the internal Pierce oscillator to the
external crystal. The oscillator provides an inverter and a feedback element. The
standard external oscillator circuitry (see figure below) comprises the crystal, two low
end capacitors and series resistor to limit the current through the crystal. The additional
LC combination is only required for 3rd overtone crystals to suppress oscillation in the
The following starting configuration is recommended to be used for the C165H:
Quarz: C
L
= 30 pF (max.), R
S
= 70 Ohm (max.), Accuracy: 96 ppm or better
External: Circuitry: C
A
= C
B
= 47 pF (max.), no serial resistor (Rx2 = 0)