Datasheet

 2010 Microchip Technology Inc. DS39935C-page 47
ENC424J600/624J600
4.6.2 UNBANKED SFR OPERATIONS
The N-byte unbanked SFR instructions are WCRU,
RCRU, BFSU and BFCU. These instructions use an
opcode with a one-byte address argument and do not
depend on the use of BxSEL instructions for SFR bank
selection.
Figure 4-6 shows the timing relationships for these
operations. Like all other opcodes, data is presented on
the SI pin, MSb first. For this class of instructions, the
first byte of data is a specific opcode; the second byte
is the 8-bit absolute address of the target SFR. If the
instruction is a write or bit set/clear opcode, the next
bytes are the data or bit mask to be written. For read
instructions, the next bytes are don’t cares.
For write and bit set/clear instructions, the SO pin is
actively driven with indeterminate ‘1’s or ‘0’s while the
CS
pin is driven low. For read instructions, random data
is clocked out on SO during SCK clocks, 1 through 16.
Starting with the 17th clock, data is clocked out
byte-wise on SO, MSb first. As with three-byte
instructions, the lower byte of a data word is presented
first, followed by the upper byte.
As long as the CS
pin is held low, the instruction
continues to execute, automatically incrementing to the
next register address in the SFR space and writing data
from SI to, or outputting data on SO from, subsequent
registers. When the end of a bank is reached, the
address continues to the top of the next bank.
Addresses continue to increment through the banks
into the unbanked SFR area (addresses 80h through
9Fh), then wrap around to the start of Bank 0 (00h). The
SFR bank value used by the BxSEL and RBSEL
opcodes is not affected by the execution of unbanked
SFR instructions.
There are four unbanked SFR opcodes, summarized in
Table 4-5. Except for addressing, the unbanked SFR
instructions are analogous to the banked SFR instruc-
tions. However, there are certain differences in their
behavior with certain pointer registers, as noted below.
FIGURE 4-6: N-BYTE SPI OPCODE (UNBANKED SFR OPERATIONS)
CS
SCK
SI
SO x x x x x x x xHi-Z
a5 a4 a3 a2 a1 a0
x x x
d00 0 c2 d7 d6 d5 d4 d3 d2 d1
x x x x x x x x x x x x x
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Opcode Unbanked SFR Address Write 1st Byte
25 26 27
D7 D6 D5
x x x
Additional
0 0 1 c1 0
CS
SCK
SI
SO x x x x x x x xHi-Z
0 0 c2
d7 d6 d5 d4 d3 d2 d1 d0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Opcode Unbanked SFR Address
Read 1st Byte
25 26 27
D7 D6 D5
Additional
0 0 1 c1 0 a5 a4 a3 a2 a1 a0
a6a7
a6a7
x x x x x x xx
Write Operation
Read Operation