Datasheet

 2006-2012 Microchip Technology Inc. . DS39662E-page 29
ENC28J60
4.2.4 WRITE BUFFER MEMORY
COMMAND
The Write Buffer Memory (WBM) command allows the
host controller to write bytes to the integrated 8-Kbyte
transmit and receive buffer memory.
If the AUTOINC bit in the ECON2 register is set, after
the last bit of each byte is written, the EWRPT Pointer
will automatically be incremented to point to the next
sequential address (Current Address + 1). If address,
1FFFh, is written with AUTOINC set, the Write Pointer
will increment to 0000h.
The WBM command is started by lowering the CS
pin.
The WBM opcode should then be sent to the
ENC28J60, followed by the 5-bit constant, 1Ah. After
the WBM command and constant are sent, the data to
be stored in the memory pointed to by EWRPT should
be shifted out MSb first to the ENC28J60. After 8 data
bits are received, the Write Pointer will automatically
increment if AUTOINC is set. The host controller can
continue to provide clocks on the SCK pin and send
data on the SI pin, without raising CS
, to keep writing to
the memory. In this manner, with AUTOINC enabled, it
is possible to continuously write sequential bytes to the
buffer memory without any extra SPI command
overhead.
The WBM command is terminated by bringing up the
CS
pin. Refer to Figure 4-6 for a detailed illustration of
the write sequence.
4.2.5 BIT FIELD SET COMMAND
The Bit Field Set (BFS) command is used to set up to
8 bits in any of the ETH Control registers. Note that this
command cannot be used on the MAC registers, MII
registers, PHY registers or buffer memory. The BFS com-
mand uses the provided data byte to perform a bit-wise
OR operation on the addressed register contents.
The BFS command is started by pulling the CS pin low.
The BFS opcode is then sent, followed by a 5-bit
address (A4 through A0). The 5-bit address identifies
any of the ETH registers in the current bank. After the
BFS command and address are sent, the data byte
containing the bit field set information should be sent,
MSb first. The supplied data will be logically ORed to
the content of the addressed register on the rising
edge of the SCK line for the D0 bit.
If the CS
line is brought high before eight bits are
loaded, the operation will be aborted for that data
byte. The BFS operation is terminated by raising the
CS
pin.
4.2.6 BIT FIELD CLEAR COMMAND
The Bit Field Clear (BFC) command is used to clear up
to 8 bits in any of the ETH Control registers. Note that
this command cannot be used on the MAC registers,
MII registers, PHY registers or buffer memory. The BFC
command uses the provided data byte to perform a bit-
wise NOTAND operation on the addressed register
contents. As an example, if a register had the contents
of F1h and the BFC command was executed with an
operand of 17h, then the register would be changed to
have the contents of E0h.
The BFC command is started by lowering the CS
pin.
The BFC opcode should then be sent, followed by a
5-bit address (A4 through A0). The 5-bit address
identifies any of the ETH registers in the current bank.
After the BFC command and address are sent, a data
byte containing the bit field clear information should
be sent, MSb first. The supplied data will be logically
inverted and subsequently ANDed to the contents of
the addressed register on the rising edge of the SCK
line for the D0 bit.
The BFC operation is terminated by bringing the CS
pin
high. If CS
is brought high before eight bits are loaded,
the operation will be aborted for that data byte.
FIGURE 4-6: WRITE BUFFER MEMORY COMMAND SEQUENCE
SO
SI
SCK
CS
0 23456789101112131415161718192021221
0011110
7654 1D0
76543210
23
32
1
Data Byte 0
Data Byte 1
Opcode Address
High-Impedance State