HMS87C1808B Datasheet, PDF (46/99 Pages) List of Unclassifed Manufacturers – 8-BIT SINGLE-CHIP MICROCONTROLLERS

HMS87C1X04B/08B/16B
The user needs to take into account variation due to tolerance of
external R and C components used.
Figure 10-4 shows how the RC combination is connected to the
HMS87C1X04B/08B/16B.
Vdd
R_EXT
X_IN
C_EXT
Cint ≈ 6pF
f_XIN÷4
X_OUT
Figure 10-4 RC Oscillator Connections
External capacitor (C_EXT) can be omitted for more cost saving.
However, the characteristics of external R only oscillation are
more variable than external RC oscillation.
V_DD
R_EXT
X_IN
C_INT ≈ 6pF
f_XIN÷4
X_OUT
The oscillator frequency, divided by 4, is output from the Xout
pin, and can be used for test purpose or to synchronize other logic.
To set the RC oscillation, it should be programmed RC_osc bit of
the configuration memory (CONFIG : 707Fh) to "1". ( Refer to
Section "21.3". )
In addition to external crystal/resonator and external RC/R oscil-
lation, the HMS81C1X04B/08B/16B provides the internal 4MHz
oscillation. The internal 4MHz oscillation needs no external
parts.
Figure 10-6 shows the pin connections in case of using the inter-
nal 4MHz oscillation as the system clock.
V_DD
X_IN
f_XIN÷4
X_OUT
Figure 10-6 Internal 4MHz Connections
To use the internal 4MHz oscillation, it should be programmed
ONPb bit and IN_CLK bit of the configuration memory (CON-
FIG : 707FH) to “0” and “1” respectively. ( Refer to Section
"21.3". )
Figure 10-5 R Oscillator Connections
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SEP. 2004 Ver 1.03