Am79C973/Am79C975
177
P R E L I M I N A R Y
EESK/LED1/SFBD pin at the end
of H_RESET. This value indi-
cates whether or not an EE-
PROM is present at the EEPROM
interface. If this bit is a 1, it indi-
cates that an EEPROM is
present. If this bit is a 0, it indi-
cates that an EEPROM is not
present.
Read accessible only. EEDET is
read only; write operations have
no effect. The value of this bit is
determined at the end of the
H_RESET operation. It is unaf-
fected by S_RESET or the STOP
bit.
Table 32 indicates the possible
combinations of EEDET and the
existence of an EEPROM and the
resulting operations that are pos-
sible on the EEPROM interface.
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
32.
Read accessible always, write
accessible only when either the
STOP or the SPND bit is set.
EEN is set to 0 by H_RESET and
is unaffected by the S_RESET or
STOP bit.
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 accessible always, write
accessible only when either the
STOP or the SPND bit is set.
ECS is set to 0 by H_RESET and
is not affected by S_RESET or
STOP.
1
ESK
EEPROM Serial Clock. This bit
and the EDI/EDO bit are used to
control host access to the EE-
PROM. Values programmed to
this bit are placed onto the EESK
pin at the rising edge of the next
clock following bit programming,
except when the PREAD bit is set
to 1 or the EEN bit is set to 0. If
both the ESK bit and the EDI/
EDO bit values are changed dur-
ing one BCR19 write operation,
Table 32. Interface Pin Assignment
RST Pin
Low
High
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
High
0
1
From EEDI Bit of
BCR19
LED0
High
0
0