SECTION 9
MASK
OPTIONS AND PROGRAMMING
The
information in this section pertains only to the MC68705R3, MC68705U3, MC68705R5, and
MC68705U5 EPROM versions
of
the M6805 Family.
9.1
MASK OPTIONS
The MC68705R3, MC68705U3, MC68705R5, and MC68705U5 mask option registers are im-
plemented
in
EPROM. Like
all
other EPROM bytes, the MOR contains all zeros prior
to
programm-
ing (if erased),
When used
to
emulate the MC6805R2 and MC6805U2, five
of
the eight MOR bits are used
in
con-
junction
with
the prescaler. Of the remaining, the
b7
bit
is
used
to
select the type
of
clock oscillator,
b3
is the secure/non-secure mode option
for
the MC68705R5/MC68705U5 only (b3
is
not
used by
the
MC68705R3/MC68705U3), and b4 is
not
used. Bits
bO,
b1, and
b2
determine the division
of
the
timer prescaler. Bit
b6
determines the timer option selection. The value
of
the TOPT
bit
(b6)
is
pro-
grammed
to
configure the TCR
(a
logic one
for
MC6805R2/ MC6805U2 emulation!.
If
the MOR timer option (TOPT) bit is a zero, the MC6805R3 and MC6805U3 are emulated. Here,
bits
b5,
b4, b2, b1, and
bO
set the initial value
of
their respective TCR bits during reset.
After
initiali-
zation the
TCR
is
software controllable.
A description
of
the MOR bits
is
as
follows:
r--:;.;b
7---,~b;;..;;6--r--..;;b;.;;.5-.,-~b4~,--..;;;.b3~r--b;;;.;;2;;......,---..;b;...;1--.,.--..;;b:...:.0--,M
ask Option
1.....1
_c_lK--1...1
T_o_p_T-LI_c_l_s-'-I_---II_s_N.-;.M_*
lL..---p_2-J..._P_1-..L._P0-.lIRegister
$F38
* MC68705R5 and MC68705U5 only.
b7,
ClK
Clock Oscillator Type
1
=
RC
0=
Crystal
NOTE
VIHTP on the TIMER (pin
8)
forces the crystal mode.
b6,
TOPT Timer Option
1 =
MC6805R2/MC6805U2type timer/prescaler. All bits, except
b6
and b7,
of
the timer
control register
(TCR) are invisible
to
the user. Bits b5, b2,
b1,
and
bO
of
the mask
option register determine the equivalent
MC6805R2/ MC6805U2 mask optio.ns.
0=
MC6805R3/MC6805U3 type timer/prescaler. All TCR bits are implemented
as
a soft-
ware programmable
timer, The state
of
bits
b5,b4,
b2,
b1,
and
bO
set the initial
values
of
their respective TCR bits (TCR
is
then software controlled after initializa-
tion).
9-1
To Next Page
Loading...
Need help?
General
