MC68HC705JP7 Datasheet, PDF (131/242 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Analog Subsystem
A/D Conversion Methods
V_CAP
V_X
t_DIS
t_DIS
(MIN)
t_DIS
(MIN)
V_MAX
t_CHG
V_X = ^{tCHG x ICHG}
C_EXT
CHG
COMP2
(TCAP)
TOF
OCF
ICF
0
1
2
31
2
Point
0
1
2
3
Action
Begin initial discharge and select mode 3
by clearing CHG and setting ATD2 and
ATD1 in the ACR. Also set ICEN bit in
ACR and IEDG bit in TCR.
V_CAP falls to V_SS. Set timer output
compare registers (OCRH and OCRL) to
desired charge start time.
Stop discharge and begin charge when
the next OCF sets the CHG control bit in
ACR.
V_CAP rises to V_X and comparator 2
output trips, setting CPF2 and CMP2,
which causes an ICF from the timer and
clears the CHG control bit in ACR. Must
clear CPF2 to trap next CPF2 flag. Load
next OCF.
Software/Hardware Action
Software write
Wait out minimum t_DIS time.
Software write to OCRH, OCRL
Timer OCF sets the CHG control
bit in the ACR.
Wait out t_CHG time.
Timer ICF clears the CHG control
bit in the ACR.
Dependent Variable(s)
Software
V_MAX, I_DIS, C_EXT,
software
Free-running timer
output compare, f_OSC
V_X, I_CHG, C_EXT
Figure 8-11. A/D Conversion — OCF/ICF Control (Mode 3)
MC68HC705JJ7 • MC68HC705JP7 — REV 4
MOTOROLA
Analog Subsystem
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Advance Information
131