Carrier Modulator Transmitter (CMT) Block Description
MC9S08RC/RD/RE/RG Data Sheet, Rev. 1.11
Freescale Semiconductor
121
8.6.3
CMT Modulator Status and Control Register (CMTMSC)
The CMT modulator status and control register (CMTMSC) contains the modulator and carrier generator
enable (MCGEN), end of cycle interrupt enable (EOCIE), FSK mode select (FSK), baseband enable
(BASE), extended space (EXSPC), prescaler (CMTDIV1:CMTDIV0) bits, and the end of cycle (EOCF)
status bit.
76543210
R
EOCF
CMTDIV1
CMTDIV0
EXSPC
BASE
FSK
EOCIE
MCGEN
W
Reset
00000000
= Unimplemented or Reserved
Figure 8-13. CMT Modulator Status and Control Register (CMTMSC)
Table 8-8. CMTMSC Field Descriptions
Field
Description
7
EOCF
End of Cycle Status Flag — The EOCF bit is set when:
The modulator is not currently active and the MCGEN bit is set to begin the initial CMT transmission.
At the end of each modulation cycle while the MCGEN bit is set. This is recognized when a match occurs
between the contents of the space period register and the down-counter. At this time, the counter is
initialized with the (possibly new) contents of the mark period buffer, CMTCMD1 and CMTCMD2. The
space period register is loaded with the (possibly new) contents of the space period buffer, CMTCMD3 and
CMTCMD4.
This ag is cleared by a read of the CMTMSC register followed by an access of CMTCMD2 or CMTCMD4.
In the case where the MCGEN bit is cleared and then set before the end of the modulation cycle, EOCF will not
be set when MCGEN is set, but will be set at the end of the current modulation cycle.
0
No end of modulation cycle occurrence since ag last cleared
1
End of modulator cycle has occurred
6:5
CMTDIV[1:0]
CMT Clock Divide Prescaler — The CMT clock divide prescaler causes the CMT to be clocked at the BUS
CLOCK frequency, or the BUS CLOCK frequency divided by 1, 2, 4, or 8. Because these bits are not double
buffered, they should not be changed during a transmission.
00 Bus clock
÷ 1
01 Bus clock
÷ 2
10 Bus clock
÷ 4
11 Bus clock
÷ 8
4
EXSPC
Extended Space Enable — The EXSPC bit enables extended space operation.
0
Extended space disabled
1
Extended space enabled
3
BASE
Baseband Enable — When set, the BASE bit disables the carrier generator and forces the carrier output high
for generation of baseband protocols. When BASE is clear, the carrier generator is enabled and the carrier output
toggles at the frequency determined by values stored in the carrier data registers. See
Section 8.5.2.2,“Baseband Mode." This bit is cleared by reset. This bit is not double buffered and should not be written to during
a transmission.
0
Baseband mode disabled
1
Baseband mode enabled
2
FSK
FSK Mode Select — The FSK bit enables FSK operation.
0
CMT operates in time or baseband mode
1
CMT operates in FSK mode