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8/01/00
Am79C976
211
P R E L I M I N A R Y
Table 90 indicates the possible
combinations of EEDET and the
existence of an EEPROM and the
resulting operations that are pos-
sible on the EEPROM interface.
Table 90. EEDET Setting
12-5
RES
Reserved locations. Written as
zeros; read as undefined.
4
EEN
EEPROM Port Enable. When this
bit is set to a 1, it causes the val-
ues of ECS, ESK, and EDI to be
driven onto the EECS, EESK,
and EEDI pins, respectively. If
EEN = 0 and no EEPROM read
function is currently active, then
EECS will be driven LOW. When
EEN = 0 and no EEPROM read
function is currently active, EESK
and EEDI pins will be driven by
the LED registers BCR5 and
BCR4, respectively. See Table
91.
Read/Write accessible. EEN is
set to 0 by H_RESET and is unaf-
fected by S_RESET or STOP.
3
RES
Reserved location. Written as
zero and read as undefined.
2
ECS
EEPROM Chip Select. This bit is
used to control the value of the
EECS pin of the interface when
the EEN bit is set to 1 and the
PREAD bit is set to 0. If EEN = 1
and PREAD = 0 and ECS is set
to a 1, then the EECS pin will be
forced to a HIGH level at the ris-
ing edge of the next clock follow-
ing bit programming.
If EEN = 1 and PREAD = 0 and
ECS is set to a 0, then the EECS
pin will be forced to a LOW level
at the rising edge of the next
clock following bit programming.
ECS has no effect on the output
value of the EECS pin unless the
PREAD bit is set to 0 and the
EEN bit is set to 1.
Read/Write accessible. ECS is
set to 0 by H_RESET and is not
affected by S_RESET or STOP.
EEDET Value
(BCR19[13])
EEPROM
Connected
Result if PREAD is Set to 1
EEPROM read operation is attempted.
Entire read sequence will occur; checksum
failure will result; PVALID is reset to 0.
EEPROM read operation is attempted.
Entire read sequence will occur; checksum
operation will pass; PVALID is set to 1.
EEPROM read operation is attempted.
Entire read sequence will occur; checksum
failure will result; PVALID is reset to 0.
EEPROM read operation is attempted.
Entire read sequence will occur; checksum
operation will pass; PVALID is set to 1.
Result of Automatic EEPROM Read
Operation Following H_RESET
First two EESK clock cycles are generated,
then EEPROM read operation is aborted
and PVALID is reset to 0.
First two EESK clock cycles are generated,
then EEPROM read operation is aborted
and PVALID is reset to 0.
EEPROM read operation is attempted.
Entire read sequence will occur; checksum
failure will result; PVALID is reset to 0.
EEPROM read operation is attempted.
Entire read sequence will occur; checksum
operation will pass; PVALID is set to 1.
0
No
0
Yes
1
No
1
Yes
Table 91. Interface Pin Assignment
Pin
*PREAD or Auto
Read in Progress
X
1
EEN
X
X
EECS
0
Active
From ECS
Bit of BCR19
0
EESK
Tri-State
Active
From ESK Bit of
BCR19
LED1
EEDI
Tri-State
Active
Low
High
High
0
1
From EEDI Bit of
BCR19
LED0
High
0
0