HD404654 Datasheet, PDF (83/111 Pages) Hitachi Semiconductor – 4-Bit Single-Chip Microcomputer

HD404654 Series
System Clock Select Registers 1 and 2 (SSR1: $029, SSR2: $02A): Four-bit write-only registers.
These registers must be set to the value specified in figures 67 and 68 depending on the frequency of the
oscillator connected to the OSC₁ and OSC₂ pins. Note that if the combination of the oscillation frequency
and the values in these registers is different from that specified in figures 67 and 68, the DTMF output
frequencies will differ from the correct frequencies as listed in Table 26.
System clock select register 1 (SSR1: $029)
Bit
Initial value
Read/Write
Bit name
3
2
1
—
—
0
—
—
W
Not used Not used SSR11
0
0
W
SSR10
× : Don’t care
System clock
SSR22 SSR11 SSR10 selection
0
0
0 400 kHz
0
0
1 800 kHz
0
1
0 2 MHz
0
1
1 4 MHz
1
×
× 3.58 MHz
Figure 67 System Clock Select Register 1 (SSR1)
Serial clock select register 2 (SSR2: $02A)
Bit
Initial value
Read/Write
Bit name
3
2
1
0
—
0
—
—
—
W
—
—
Not used SSR22 Not used Not used
SSR22 System clock selection
0 Selected from 400 kHz, 800 kHz,
2 MHz, 4 MHz ^*
1 3.58 MHz
Note: * Refer to system clock select register 1 (SSR1).
Figure 68 System Clock Select Register 2 (SSR2)
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