PIC18FXX20
DS39583C-page 6 2010 Microchip Technology Inc.
2.6 Serial Program/Verify Operation
The SCLK pin is used as a clock input pin and the
SDATA pin is used for entering command bits and data
input/output during serial operation. Commands and
data are transmitted on the rising edge of SCLK,
latched on the falling edge of SCLK, and are Least
Significant bit (LSb) first.
2.6.1 4-BIT COMMANDS
All instructions are 20-bits, consisting of a leading 4-bit
command followed by a 16-bit operand, which depends
on the type of command being executed. To input a
command, SCLK is cycled four times. The commands
needed for programming and verification are shown in
Table 2-3.
Depending on the 4-bit command, the 16-bit operand
represents 16 bits of input data, or 8 bits of input data
and 8 bits of output data.
Throughout this specification, commands and data are
presented as illustrated in Figure 2-4. The 4-bit
command is shown MSb first. The command operand,
or “Data Payload”, is shown <MSB><LSB>. Figure 2-7
demonstrates how to serially present a 20-bit
command/operand to the device.
2.6.2 CORE INSTRUCTION
The core instruction passes a 16-bit instruction to the
CPU core for execution. This is needed to setup
registers as appropriate for use with other commands.
TABLE 2-3: COMMANDS FOR
PROGRAMMING
TABLE 2-4: SAMPLE COMMAND
SEQUENCE
FIGURE 2-7: TABLE WRITE, POST-INCREMENT TIMING (1101)
Description
4-Bit
Command
Core Instruction
(Shift in16-bit instruction)
0000
Shift out TABLAT register 0010
Table Read 1000
Table Read, post-increment 1001
Table Read, post-decrement 1010
Table Read, pre-increment 1011
Table Write 1100
Table Write, post-increment by 2 1101
Table Write, post-decrement by 2 1110
Table Write, start programming 1111
4-Bit
Command
Data
Payload
Core Instruction
1101 3C 40 Table Write,
post-increment by 2
1234
SCLK
P5
SDATA
SDATA = Input
5678 1
234
P5A
9
10 11 13 15 161412
Fetch Next 4-bit Command
1011
1234
nnnn
P3
P2
P2A
000000 010001111 0
04C3
P4
4-bit Command 16-bit Data Payload
P2B
