PIC17CXX Datasheet, PDF (7/16 Pages) Microchip Technology – EPROM Memory Programming Specification

EPROM Memory Programming Specification
4.0 CONFIGURATION WORD
Configuration bits are mapped into program memory.
Each bit is assigned one memory location. In erased
condition a bit will read as '1'. To program a bit, the user
needs to write to the memory address. The data is
immaterial; the very act of writing will program the bit.
The configuration word locations are shown in
Table 4-3. The programmer should not program the
reserved locations to avoid unpredictable results
and to be compatible with future variations of the
PIC17C4X. It is also mandatory that configuration
locations are programmed in the strict order start-
ing from the first location (0xFE00) and ending with
the last (0xFE0F). Unpredictable results may occur
if the sequence is violated.
4.1 Reading Configuration Word
The PIC17CXX has seven configuration locations (see
Table 4-1). These locations can be programmed (read
as '0') or left unprogrammed (read as '1') to select var-
ious device configurations. Any write to a configuration
location, regardless of the data, will program that con-
figuration bit. Reading any configuration location
between 0xFE00 and 0xFE07 will place the low byte of
the configuration word (see Table 4-2) into PAD<7:0>
(PORTC). PAD<15:8> (PORTB) will be set to 0xFF.
Reading a configuration location between 0xFE08 and
0xFE0F will place the high byte of the configuration
word into PAD<7:0> (PORTC). PAD<15:8> (PORTB)
will be set to 0xFF.
TABLE 4-1: CONFIGURATION BIT
PROGRAMMING LOCATIONS
Bit
Address
FOSC0
0xFE00
FOSC1
0xFE01
WDTPS0
0xFE02
WDTPS1
0xFE03
PM0
0xFE04
PM1
0xFE06
PM2^†
0xFE0F
†_{This location does not exist on the PIC17C42.}
TABLE 4-2: READ MAPPING OF CONFIGURATION BITS
15 14 13 12 11 10 9
1111111
8 76 5 4
3
2
1
0
1 — PM1 — PM0 WDTPS1 WDTPS0 FOSC1 FOSC0
15 14 13 12 11 10 9 8 7 6 5 4
3
2
1
0
1 1 1 1 1 1 1 1 PM2* — — —
—
—
—
—
—=Unused
PM<2:0>, Processor Mode Select bits
111 = Microprocessor mode
110 = Microcontroller mode
101 = Extended Microcontroller mode
000 = Code protected microcontroller mode
WDTPS<1:0>, WDT Prescaler Select bits.
11 = WDT enabled, postscaler = 0
10 = WDT enabled, postscaler = 256
01 = WDT enabled, postscaler = 64
00 = WDT disabled, 16-bit overflow timer
FOSC<1:0>, Oscillator Select bits
11 = EC oscillator
10 = XT oscillator
01 = RC oscillator
00 = LF oscillator
* _{This bit does not exist on PIC17C42.}
© 1996 Microchip Technology Inc.
DS30139I-page 7