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CHAPTER 7 REGISTERS
343
(22) Idle cell (empty cell) count register (IDLCT)
7
0
Address
Default
R/W
IDLCT
15H
00H
R
IDLC[1:0] = 10
IDLC[1:0] = 01
IDLC[1:0] = 00
23
19
16 15
8
7
0
IDLCNTR
0
0
0
0
The SMP bit is set to 1
19
16 15
8
7
0
Idle cell counter
This is a window register that is used to read the contents of the 20-bit
IDLCNTR
register by reading eight
bits, eight bits, and four bits, three times. First, the low-order eight bits (
IDLCNTR[7:0]
) are read, then the
middle eight bits (
IDLCNTR[15:8]
), and finally the high-order four bits (
IDLCNTR[19:16]
). Which of the
low-order, middle, or high-order bits is read is indicated by the
IDLC1
and
IDLC0
bits of the
PCPR2
register (address: 1AH). For each of these bits, the default value is 00. Each time the
IDLCT
register is
read, the value of these bits is automatically changed in the order of 00 -> 01 -> 10 -> 00 -> 01.
IDLCNTR
is a load register that is used to sample (store) the value of the idle cell counter. By setting the
SMP
bit of the
PCSR
register (address: 1BH) to 1, the value of the
idle cell counter
is stored into the
IDLCNTR
register. This value indicates the number of idle cells (empty cells) that have been received
since the contents of the
idle cell counter
were last sampled. The value stored into the
IDLCNTR
register
is held until the
idle cell counter
is next sampled.
Sampling the contents of the
idle cell counter
causes the counter to be cleared to 0. The counter is also
cleared to 0 when the
IDLC
bit of the
PCIR2
register (address: 1DH) is set to 1.
When the value of the counter is all F, the
IDLC
bit of the
PCOCR2
register (address: 21H) is set to 1 to
indicate a counter overflow being detected. Also, the
PCO
bit of the
PICR
register (address: 06H) is set to
1, thus causing an interrupt. After the occurrence of an overflow, the
idle cell counter
again starts to
count up from 0.