Serial Communications Interface Module (SCI)
I/O Registers
MC68HC908MR16/MC68HC908MR32 — Rev. 4.0 Advance Information
MOTOROLA Serial Communications Interface Module (SCI) 305
SCP1 and SCP0 — SCI Baud Rate Prescaler Bits
These read/write bits select the baud rate prescaler divisor as shown
in Table 14-5. Reset clears SCP1 and SCP0.
SCR2–SCR0 — SCI Baud Rate Select Bits
These read/write bits select the SCI baud rate divisor as shown in
Table 14-6. Reset clears SCR2–SCR0.
Use this formula to calculate the SCI baud rate:
where:
fOP = internal operating frequency
PD = prescaler divisor
BD = baud rate divisor
Table 14-7 shows the SCI baud rates that can be generated with a
4.9152-MHz crystal with the CGM set for an fOP of 7.3728 M Hz and th e
CGM set for an fOP of 4.9152 MHz.
Table 14-5. SCI Baud Rate Prescaling
SCP1:SCP0 Prescaler Divisor (PD)
00 1
01 3
10 4
11 13
Table 14-6. SCI Baud Rate Selection
SCR2:SCR1:SCR0 Baud Rate Divisor (BD)
000 1
001 2
010 4
011 8
100 16
101 32
110 64
111 128
Baud rate fOP
64 PD BD××
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