PIC16F87 datasheet(8/24 Pages) MICROCHIP

8 / 24 page

PIC16F87/88

DS39607B-page 8

 2002 Microchip Technology Inc.

3.4.2

SERIAL PROGRAM OPERATION

The RB6 pin is used as a clock input pin, while the RB7

pin is used to enter command bits, and input or output

data during serial operation. To input a command, the

clock pin (RB6) is cycled six times. Each command bit

is latched on the falling edge of the clock, with the Least

Significant bit (LSb) of the command being input first.

The data on RB7 is required to have a minimum setup

(tset1)

and

hold

(thold1)

time

(see

AC/DC

specifications), with respect to the falling edge of the

clock. Commands with associated data (read and load)

are specified to have a minimum delay (tdly1) of 1

µs

between the command and the data. After this delay,

the clock pin is cycled 16 times, with the first cycle

being a Start bit (0) and the last cycle being a Stop bit

(0). Data is transferred LSb first.

During a read operation, the LSb will be transmitted

onto RB7 on the rising edge of the second cycle, while,

during a load operation, the LSb will be latched on the

falling edge of the second cycle. A minimum 1

µs delay

(tdly2) is specified between consecutive commands.

All commands and data words are transmitted LSb first.

The data is transmitted on the rising edge and latched

on the falling edge of the clock. To allow decoding of

commands and reversal of data pin configuration, a

time separation of at least 1

µs (tdly1) is required

between a command and a data word, or another

command.

The available commands are described in the following

paragraphs and listed in Table 3-1.

3.4.2.1

Load Configuration

Upon receipt of the Load Configuration command, the

PC will be set to 0x2000 and the data sent with the

command is discarded. The four ID locations and the

configuration words can then be programmed using the

normal programming sequence, as described in

Section 3.4 “Program Mode”. A description of the

memory mapping schemes of the program memory for

normal operation and Configuration mode operation is

shown in Figure 3-1. Once the configuration memory is

entered, the only way to get back to the user program

memory is to exit the Program/Verify Test mode by

taking MCLR low (VIL).

3.4.2.2

Load Data for Program Memory

After receiving this command, the chip will load one

word (with 14 bits as a “data word”) to be programmed

into user program memory when 16 cycles are applied.

A timing diagram for this command is shown in

Figure 7-1.

3.4.2.3

Load Data for Data Memory

After receiving this command, the chip will load a 14-bit

“data word” when 16 cycles are applied. However, 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 (8 data bits and 6 zeros). 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

protected, the data is read as all zeros. A timing

diagram for this command is shown in Figure 7-2.

3.4.2.4

Read Data from Program Memory

After receiving this command, the chip will transmit

data bits out of the program memory (user or

configuration) currently accessed, starting with the

second rising edge of the clock input. The RB7 pin will

go into Output mode on the second rising clock edge,

reverting to Input mode (high-impedance) after the 16th

rising edge. A timing diagram of this command is

shown in Figure 7-3.

3.4.2.5

Read Data from Data Memory

After receiving this command, the chip will transmit

data bits out of the data memory, starting with the

second rising edge of the clock input. The RB7 pin will

go into Output mode on the second rising edge,

reverting to Input mode (high-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. A timing diagram for this

command is shown in Figure 7-4.

3.4.2.6

Increment Address

The PC is incremented when this command is

received. A timing diagram of this command is shown

in Figure 7-5.

Note:

Upon entering Programming mode, a

“Load Data for Program Memory” or “Load

Data for Data Memory” command of 0x01

must be given before a Begin Erase or

Begin Programming command is initiated.

This will ensure that the programming

pointer is pointing to the correct location in

data or program memory.

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