AT89LP51 datasheet(82/113 Pages) ATMEL

82 / 113 page

3709B–MICRO–12/10

AT89LP51/52 - Preliminary

17.3

Command Format

Programming commands consist of an opcode byte, two address bytes, and zero or more data

bytes. Figure 17-4 on page 82 shows a simplified flow chart of a command sequence.

A sample command packet is shown in Figure 17-5 on page 83. The SS pin defines the packet

frame. SS must be brought low before the first byte in a command is sent and brought back high

after the final byte in the command has been sent. The command is not complete until SS

returns high. Command bytes are issued serially on MOSI. Data output bytes are received seri-

ally on MISO. Packets of variable length are supported by returning SS high when the final

required byte has been transmitted. In some cases command bytes have a don’t care value.

Don’t care bytes in the middle of a packet must be transmitted. Don’t care bytes at the end of a

packet may be ignored.

Page oriented instructions always include a full 16-bit address. The higher order bits select the

page and the lower order bits select the byte within that page. The AT89LP51/52 allocates 6 bits

for byte address, 1 bit for low/high half page selection and 9 bits for page address. The half page

to be accessed is always fixed by the page address and half select as transmitted. The byte

address specifies the starting address for the first data byte. After each data byte has been

transmitted, the byte address is incremented to point to the next data byte. This allows a page

command to linearly sweep the bytes within a page. If the byte address is incremented past the

last byte in the half page, the byte address will roll over to the first byte in the same half page.

While loading bytes into the page buffer, overwriting previously loaded bytes will result in data

corruption.

For a summary of available commands, see Table 17-2 on page 84.

Figure 17-4. Command Sequence Flow Chart

Input Opcode

Input Address

High Byte

Input Address

Low Byte

Input/Output

Data

Address +1

Byte Mode or

Count == 64

yes

AT89LP51 데이터시트(PDF) 82 Page - ATMEL Corporation