Motorola MC6805R Series Advance Information page 57

necessary control bits to allow programming the EPROM. The bootstrap program manipulates the
PCR when programming so that users need not be concerned with the PCR in most applications. A
description of each bit follows.
b7
b6 b5
b4
b3 b2 b1 bO Programming
I
VPON
I
PGE
I
PLE IControl
Register $008
bO,
PIE
Programming Latch Enable - When cleared, this bit allows the address and data to be
latched into the EPROM. When this bit is set, data can be read from the EPROM.
1 = (set) read EPROM
0= (clear) latch address and data into EPROM (read disable)
PLE is set during a reset, but may be cleared any time. However, its effect on the
EPROM is inhibited if VPON is a logic one.
b1,
J5GE
Program Enable - When cleared,
f5GE
enables programming of the EPROM. PGE can
only be cleared if
PIT
is cleared. PGE must be set when changing the address and data;
i.e., setting up the byte to be programmed.
1 = (set) inhibit EPROM programming
0= (clear) enable EPROM programming (if
PIE
is low)
PGE
is set during a reset; however, it has no effect on EPROM circuits if VPON is a logic
one.
b2, VPON (Vpp ON) - VPON is a read-only bit and when at a logic zero it indicates that a "high
voltage" is present at the Vpp pin.
1 = no "high voltage" on Vpp pin
0= "high voltage" on Vpp pin
VPON being one "disconnects" PGE and PLE from the rest of the chip, preventing acci-
dental clearing of these bits from affecting the normal operating mode .
. NOTE
VPON being zero does not indicate that the Vpp level is correct for
programming. It is used as a safety interlock for the user in the
normal operating mode.
The programming control register functions are shown below.
VPON PGE PLE Programming Conditions
a a
a
Programming mode (program EPROM byte)
1
a
o
PG E and PLE disabled from system
a
1
a
Programming disabled (latch address and data in EPROM)
1 1
a
PG E and
'PIE
disabled from system
a a
1 Invalid state; PGE=O iff
PIT
=
a
1
a
1 Invalid state; PGE=O iff
PIT
=
a
a
1 "High voltage" on Vpp
1
1 PGE and PLE disabled from system (operating mode)
9-3