MC68HC05BD3 Datasheet, PDF (103/112 Pages) Motorola, Inc – HCMOS microcontroller

14.3.1 Programming Control Register (PCR)
The EPROM Programming Control register controls the actual programming of the EPROM in the
MC68HC705BD3.
Address bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
State
on reset
$001D
ELAT PGM ---- --00
ELAT - EPROM Latch Control
1 (set) –
0 (clear) –
EPROM address and data bus configured for programming (writes to
EPROM cause address data to be latched). EPROM is in
programming mode and cannot be read if ELAT is 1. This bit is not
able be set when no V_PP voltage is applied to the V_PP pin.
EPROM address and data bus configured for normal reads.
PGM - EPROM Program Command
1 (set) – Programming power switched on to EPROM array. If ELAT≠1 then
PGM = 0.
0 (clear) – Programming power switched off to EPROM array.
14.3.2 EPROM Programming Sequence
Programming the EPROM of the MC68HC705BD3 is as follows:
1) Set the ELAT bit.
2) Write the data to be programmed to the address to be programmed.
3) Set the PGM bit.
4) Delay for the appropriate amount of time.
5) Clear the PGM and the ELAT bits.
The last action may be carried out in a single CPU write operation. It is important to remember
that an external programming voltage must be applied to the V_PP pin while programming, but
should be equal to V_DD during normal operation.
Example shows address $2000 is programmed with $00.
CLR
LDX
BSET
LDA
STA
PCR
#$00
1,PCR
#$00
$2000,X
;reset PCR
;load index register with 00
;set ELAT bit
;load data=00 in to A
;latch data and address
14
MC68HC05BD3
MC68HC705BD3
TPG
MOTOROLA
14-3