Mask Options - Motorola MC6805R Series Advance Information

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