參數(shù)資料
型號: HSP50214
廠商: Intersil Corporation
英文描述: Programmable Downconverter
中文描述: 可編程變頻器
文件頁數(shù): 33/54頁
文件大?。?/td> 395K
代理商: HSP50214
33
Suppose the depth of the Buffer RAM Output section is pro-
grammed for an INTRRP pointer depth of 4. If the output is at 4
times the baud rate, the processing routine for the microprocessor
may only need to read the buffer when the Buffer RAM had 4
samples since processing is usually on a baud by baud basis.
Figure 37 illustrates the conceptual view of the FIFO as a circular
buffer, with the Write address one step ahead of the read
address.
Figure 37A deals with clockwise read and write address incre-
menting. The FIFO depth is the difference between the Write and
Read pointers, modulo 8. Figure 37B illustrates a FIFO status of
Full, while Figure 37C illustrates a FIFO empty status condition.
Figure 37D illustrates a programmed FIFO depth of 3 and the
INTRRP signal indicating that the buffer has sufficient data to be
read.Following some simple rules for operating the FIFO will elim-
inate most operational errors:
Rule #1: The Read and Write Pointers cannot point at the same
address (the circuitry will not allow this).
Rule #2: The FIFO is full when the Write Address = Read
Address -1 (no more data will be written until some samples are
read or the FIFO is reset).
Rule #3: The FIFO is empty when the Read Address = (Write
Address -1) (the circuitry will not allow the read pointer to be
incremented).
Rule #4: You cannot write over what you have not read.
Rule #5: RESET places the Write address pointer = 000 and
Read address pointer = 111.
Rule #6: The best addressing scheme is to read the FIFO until it
is empty. This avoids erroneous INTRRP assertions and provides
for simple FIFO depth monitoring. The interrupt is generated
when the depth increments past the threshold
.
H
INTRRP
OEAL
OEBL
PDC
16-BIT
μ
P
SEL(2:0)
BOUT(7:0)
AOUT(7:0)
FIGURE 35. INTERFACE BETWEEN A 16-BIT MICROPROCES-
SOR AND PDC IN FIFO BUFFER RAM MODE
INT
RD
D(15:8)
D(7:0)
A(2:0)
1
2 3 4
1 2 3 4
5 6 7 8
0
1
4
7
0
1
INTRRP
OEAL,
OEBL
SEL(0:2)
I
Q
FR
I
Q
AOUT(7:0),
BOUT(7:0)
PROCCLK
8 CLKS
> 4 CLKS
FIGURE 36. TIMING DIAGRAM FOR PDC IN FIFO MODE WITH
OUTPUTS I, Q, AND FREQUENCY SENT TO
AOUT(7:0) AND BOUT(7:0)
FIGURE 37. FIFO REGISTER OPERATION
READ
WRITE
FIFO
DEPTH
WRITE
READ
READ
WRITE
WRITE
READ
READY
A: FIFO DEPTH IS (WRITE - READ)
B: FIFO FULL IS WHEN (WRITE - READ) = 7
C: FIFO EMPTY IS WHEN (WRITE - READ) = 1
D: FIFO READY IS WHEN (WRITE - READ) > DEPTH
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
HSP50214
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