defined after H_RESET, and is
unaffected by S_RESET and the
STOP bit.
BCR48: LED4 Status
This register defines the functionality of LED4. LED4
will default to indicating the selected SPEED with Pulse
stretching enabled (default = 0082h).
BCR47: OnNow Pattern Matching Register 3
BCR48 controls the function(s) that the LED4 pin dis-
plays. Multiple functions can be simultaneously en-
abled on this LED pin. The LED display will indicate the
logical OR of the enabled functions.
Note: This register is used to control and indirectly ac-
cess the Pattern Match RAM (PMR). When BCR45 is
written and the PMAT_MODE bit (bit 7) is 1, Pattern
Match logic is enabled. No bus accesses into PMR are
possible, and BCR46, BCR47, and all other bits in
BCR45 are ignored. When PMAT_MODE is set, a read
of BCR45, BCR46, or BCR47 returns all undefined bits
except for PMAT_MODE.
Note: When LEDPE (BCR2, bit 12) is set to 1, pro-
gramming of the LED2 Status register is enabled.
When LEDPE is cleared to 0, programming of the
LED2 register is disabled. Writes to those registers will
be ignored.
When BCR45 is written and the PMAT_MODE bit is 0,
the Pattern Match logic is disabled and accesses to the
PMR are possible. Bits 6-0 of BCR45 specify the ad-
dress of the PMR word to be accessed. Following the
write to BCR45, the PMR word may be read by reading
BCR45, BCR46 and BCR47 in any order. To write to
PMR word, the write to BCR45 must be followed by a
write to BCR46 and a write to BCR47 in that order to
complete the operation. The RAM will not actually be
written until the write to BCR47 is complete. The write
to BCR47 causes all 5 bytes (four bytes of BCR46-47
and the upper byte of the BCR45) to be written to what-
ever PMR word is addressed by bits 6:0 of BCR45.
Note: Bits 15-0 in this register are programmable
through the EEPROM PREAD operation.
Bit
Name
Description
31-16 RES
Reserved locations. Written as
zeros and read as undefined.
15
LEDOUT
This bit indicates the current
(non-stretched) value of the LED
output pin. A value of 1 in this bit
indicates that the OR of the en-
abled signals is true.
When PMAT_MODE is 0, the contents of the word ad-
dressed by bits 6:0 of BCR45 can be read by reading
BCR45-47 in any order.
The logical value of the LEDOUT
status signal is determined by the
settings of the individual Status
Enable bits of the LED register
(bits 8 and 6-0).
Bit
Name
Description
31-16 RES
Reserved locations. Written as
zeros and read as undefined.
Read accessible always. This bit
is read only; writes have no ef-
fect. LEDOUT is unaffected by
H_RESET, S_RESET, or STOP.
15-8 PMR_B4
Pattern Match RAM Byte 4. This
byte is written into or read from
Byte 4 of Pattern Match RAM.
14
LEDPOL
LED Polarity. When this bit has
the value 0, then the LED pin will
be driven to a LOW level whenev-
er the OR of the enabled signals
is true, and the LED pin will be
disabled and allowed to float high
whenever the OR of the enabled
signals is false (i.e., the LED out-
put will be an Open Drain output
and the output value will be the
inverse of the LEDOUT status
bit).
These bits are read and write ac-
cessible always. PMR_B4 is un-
defined after H_RESET, and is
unaffected by S_RESET and the
STOP bit.
7-0
PMR_B3
Pattern Match RAM Byte 3. This
byte is written into or read from
Byte 3 of Pattern Match RAM.
These bits are read and write ac-
cessible always. PMR_B3 is un-
defined after H_RESET, and is
unaffected by S_RESET and the
STOP bit.
When this bit has the value 1,
then the LED pin will be driven to
a HIGH level whenever the OR of
the enabled signals is true, and
the LED pin will be driven to a
LOW level whenever the OR of
the enabled signals is false (i.e.,
176
Am79C978
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