16F874 datasheet(6/22 Pages) MICROCHIP

6 / 22 page

PIC16F87X

DS39025F-page 6

 2002 Microchip Technology Inc.

2.4.2.3

Load Data for Data Memory

After receiving this command, the chip will load in a

14-bit “data word” when 16 cycles are applied. How-

ever, the data memory is only 8-bits wide, and thus,

only the first 8-bits of data after the START bit will be

programmed into the data memory. It is still necessary

to cycle the clock the full 16 cycles in order to allow the

internal circuitry to reset properly. The data memory

contains up to 256 bytes. If the device is code pro-

tected, the data is read as all zeros.

2.4.2.4

Read Data from Program Memory

After receiving this command, the chip will transmit

data bits out of the program memory (user or configu-

ration) currently accessed, starting with the second ris-

ing edge of the clock input. The RB7 pin will go into

Output mode on the second rising clock edge, and it

will revert back to Input mode (hi-impedance) after the

16th rising edge. A timing diagram of this command is

shown in Figure 6-2.

2.4.2.5

Read Data from Data Memory

After receiving this command, the chip will transmit

data bits out of the data memory starting with the sec-

ond rising edge of the clock input. The RB7 pin will go

into Output mode on the second rising edge, and it will

revert back to Input mode (hi-impedance) after the 16th

rising edge. As previously stated, the data memory is

8-bits wide, and therefore, only the first 8-bits that are

output are actual data.

2.4.2.6

Increment Address

The PC is incremented when this command is

received. A timing diagram of this command is shown

in Figure 6-3.

2.4.2.7

Begin Erase/Program Cycle

A load command must be given before every begin

programming command. Programming of the appro-

priate memory (test program memory, user program

memory or data memory) will begin after this command

is received and decoded. An internal timing mechanism

executes an erase before write. The user must allow for

both erase and programming cycle times for program-

ming to complete. No “end programming” command is

required.

2.4.2.8

Begin Programming

A load command must be given before every begin

programming command. Programming of the appro-

priate memory (test program memory, user program

memory or data memory) will begin after this command

is received and decoded. An internal timing mechanism

executes a write. The user must allow for program

cycle time for programming to complete. No “end pro-

gramming” command is required.

This command is similar to the ERASE/PROGRAM

CYCLE command, except that a word erase is not

done. It is recommended that a bulk erase be per-

formed before starting a series of programming only

cycles.

Note:

The Begin Program operation must take

place at 4.5 to 5.5 VDD range.

TABLE 2-2:

COMMAND MAPPING FOR PIC16F87X

Command

Mapping (MSB … LSB)

Data

Voltage

Range

Load Configuration

0000

0, data (14), 0

2.2V - 5.5V

Load Data for Program Memory

0010

0, data (14), 0

2.2V - 5.5V

Read Data from Program Memory

0100

0, data (14), 0

2.2V - 5.5V

Increment Address

0110

2.2V - 5.5V

Begin Erase Programming Cycle

1000

2.2V - 5.5V

Begin Programming Only Cycle

1000

4.5V - 5.5V

Load Data for Data Memory

0011

0, data (14), 0

2.2V - 5.5V

Read Data from Data Memory

0101

0, data (14), 0

2.2V - 5.5V

Bulk Erase Setup1

0001

4.5V - 5.5V

Bulk Erase Setup2

0111

4.5V - 5.5V

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