Rainbow Electronics DS25LV02 - Manual (Page 5)

DS25LV02: Low-Voltage 1024-Bit EPROM
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EPROM MEMORY DATA FIELD
The DS25LV02 has a linear address space for access to the EPROM data field. The EPROM data field is
organized as 4 pages of 32 bytes each as shown in Table 1. The Read Memory and Read Data/Generate CRC
Memory function commands provide read access to the 1024 bits of the EPROM data field. The Write Memory
function command provides write access to the EPROM data field. When received from the factory, the entire
1024-bit EPROM data field is erased and returns logical 1’s when read. Bits within the data field are one time
programmable. Programming changes the bit value to logical zero from the factory default erased value of a logical
1. Once a bit is programmed, it cannot be set back to a logical 1.
Table 1. EPROM Data Field
ADDRESS (HEX) DESCRIPTION READ/WRITE
0000–001F PAGE 0 (32 bytes) R/W*
0020–003F PAGE 1 (32 bytes) R/W*
0040–005F PAGE 2 (32 bytes) R/W*
0060–007F PAGE 3 (32 bytes) R/W*
0080–FFFF Reserved
* One-time write to “0” for each bit.
READ MEMORY [F0h]
The Read Memory command is used to read data from PAGE 0 to PAGE 3 of the 1024-bit EPROM data field. The
bus master follows the command byte with a 2-byte address (TA1 = (T7:T0), TA2 = (T15:T8)) that indicates a
starting byte location within the data field. An 8-bit CRC of the command byte and address bytes is computed by
the DS25LV02 and read back by the bus master to confirm that the correct command word and starting address
were received. If the CRC is deemed to be incorrect by the bus master, the bus master should issue a reset pulse
and repeat the entire sequence. If the CRC is deemed to be correct by the bus master, read time slots can be
issued to receive data from the EPROM data field starting at the initial address. The bus master can issue a reset
pulse at any point or continue to issue read time slots until the end of PAGE 3 of the data field is reached.
If reading continues through the end of PAGE 3, the bus master can issue eight additional read time slots and the
DS25LV02 will respond with a 8-bit CRC of all data bytes read from the initial starting byte through the last byte of
PAGE 3. Terminating the command transaction with a reset pulse prior to reaching the end of PAGE 3 results in a
loss of availability of the 8-bit CRC.
READ DATA/GENERATE 8-BIT CRC [C3h]
The Read Data/Generate 8-bit CRC command is used to read data from PAGE 0 to PAGE 3 of the 1024-bit
EPROM data field. The bus master follows the command byte with a 2-byte address
(TA1 = (T7:T0), TA2 = (T15:T8)) that indicates a starting byte location within the data field. An 8-bit CRC of the
command byte and address bytes is computed by the DS25LV02 and read back by the bus master to confirm that
the correct command word and starting address were received. If the CRC is deemed to be incorrect by the bus
master, the bus master should issue a reset pulse and repeat the entire sequence. If the CRC is deemed to be
correct by the bus master, read time slots can be issued to receive data from the EPROM data field starting at the
initial address. The bus master can issue a reset pulse at any point or continue to issue read time slots until the
end of the 32-byte page is reached. If reading occurs through the end of the 32-byte page, the bus master can
issue eight additional read time slots and the DS25LV02 will respond with an 8-bit CRC of all data bytes read from
the initial starting byte through the last byte of the current page. After the CRC is received, additional read time
slots return data starting with the first byte of the next page. This sequence will continue until the bus master reads
PAGE 3 and its accompanying CRC. Thus each page of data can be considered to be 33 bytes long: the 32 bytes
of user-programmed EPROM data and an 8-bit CRC that gets generated automatically at the end of each page.
The Read Data/Generate 8-Bit CRC command sequence can be exited at any point by issuing a reset pulse.