
2009 Microchip Technology Inc.
Advance Information
DS41297F-page 27
PIC18F2XK20/4XK20
FIGURE 4-4:
SHIFT OUT DATA HOLDING REGISTER TIMING DIAGRAM (0010)
FIGURE 4-5:
HIGH-IMPEDANCE DELAY
4.5
Verify Data EEPROM
A data EEPROM address may be read via a sequence
of core instructions (4-bit command, ‘0000’) and then
output on PGD via the 4-bit command, ‘0010’ (TABLAT
register).
The
result
may
then
be
immediately
compared to the appropriate data in the programmer’s
reading data EEPROM.
4.6
Blank Check
The term “Blank Check” means to verify that the device
has no programmed memory cells. All memories must
be verified: code memory, data EEPROM, ID locations
and Configuration bits. The device ID registers
(3FFFFEh:3FFFFFh) should be ignored.
A “blank” or “erased” memory cell will read as a ‘1’.
Therefore, Blank Checking a device merely means to
verify that all bytes read as FFh except the Configura-
tion bits. Unused (reserved) Configuration bits will read
‘0’ (programmed). Refer to
Table 5-1 for blank configu-
ration expect data for the various PIC18F2XK20/
4XK20 devices.
Given that Blank Checking is merely code and data
EEPROM verification with FFh expect data, refer to
for implementation details.
FIGURE 4-6:
BLANK CHECK FLOW
12
3
4
PGC
P5
PGD
PGD = Input
Shift Data Out
P6
PGD = Output
56
7
8
1
23
4
P5A
910
11
13
15
16
14
12
Fetch Next 4-bit Command
01
0
PGD = Input
LSb
MSb
12
34
56
12
3
4
nn
n
P14
(Note 1)
Note
1:
Magnification of the High-Impedance delay between PGC and PGD is shown in
Figure 4-5.(Note 1)
MSb
nn
1
2
P19
PGD
PGC
P3
Yes
No
Start
Blank Check Device
Is
device
blank?
Continue
Abort