Page 175 - Programming Microcontrollers in C

160 Chapter 4 Small 8-Bit Systems

effect after this bit is erased until after the next
chip reset.
Control of the EEPROM programming is through the EEPROMCTL
register found at address 0x07. The bits in this register are as follows:

EEPCTL/CLK Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
0x07 0 0 0 0 ECLK E1ERA E1LAT E1PGM

E1PGM Bit 0 EEPROM Program Bit. This bit turns the internal
Vpp charge pump on and off. When this bit is 0,
the charge pump is turned off, and when it is at 1,
the charge pump is turned on. The charge pump
voltage can be measured on the pin Vpp1. This bit
cannot be set until after the program data are latched
in place by asserting the E1LAT bit. Resetting the
E1LAT bit will also reset the E1PGM bit.
E1LAT Bit 1 EEPROM Data/Address Latch. When this bit is re­
set to zero, both the E1PGM bit and the E1ERA bit
are reset to zero. When the E1LAT bit is reset, data
can be read from the EEPROM. The first data write
to the EEPROM array after this bit is set is latched
until the E1LAT bit is reset. Data can be latched
only when the E1PGM bit is reset to zero. This op­
eration allows programming of the EEPROM.
E1LAT is automatically reset when the chip is reset
or when the STOP instruction is executed.
E1ERA Bit 2 EEPROM Erase Bit. If the bit E1ERA is reset to
zero when E1LAT and E1PGM are set to one, data
are programmed into the EEPROM. Otherwise,
if E1ERA is set to one and E1LAT and E1PGM
are set to one, the specified address in the
EEPROM will be erased. E1ERA cannot be set
before E1LAT, and resetting E1LAT to zero will
cause E1ERA to be reset.
Let us now examine a possible sequence of code that can be used
to program and erase locations in EEPROM. First, several macro
definitions should be used to define the various parameters used.