IDT72511 Ver la hoja de datos (PDF) - Integrated Device Technology
Número de pieza
componentes Descripción
Lista de partido
IDT72511 Datasheet PDF : 28 Pages
| |||
IDT72511/IDT72521
BIDIRECTIONAL FIRST-IN FIRST-OUT MEMORY
MILITARY AND COMMERCIAL TEMPERATURE RANGES
Port B Interface
Port B has reread/rewrite and DMA functions. Port B can
be configured to interface to either Intel-style (RB, WB) or
Motorola-style (DSB, R/WB) devices in Configuration Register
5 (see Table 10). Port B can also be configured to talk to a
processor or a peripheral device through Configuration Reg-
ister 5. In processor interface mode, the Port B interface
controls are inputs. In peripheral interface mode, the Port B
interface controls are outputs. After a hardware reset or a
software Reset All command, Port B defaults to an Intel-style
processor interface; the controls are inputs.
DMA Control Interface
The BiFIFO has DMA control to simplify data transfers with
peripherals. For the BiFIFO DMA controls (REQ, ACK and
CLK) to operate, the BiFIFO must be in peripheral interface
mode (Configuration Register 5, Table 10).
DMA timing is controlled by the external clock input, CLK.
An internal clock is derived from this CLK signal to generate
the RB, WB, DSB and R/WB output signals. The internal clock
also determines the timing between REQ assertion and ACK
assertion. Bit 9 of Configuration Register 5 determines whether
the internal clock is the same as CLK or whether the internal
clock is CLK divided by 2.
Bit 8 of Configuration Register 5 set whether RB, WB and
DSB are asserted for 1 or 2 internal clocks. Bits 6 and 7 of
Configuration Register 5 set the number of clocks between
REQ assertion and ACK assertion. The clocks between REQ
assertion and ACK assertion can be 2, 3, 4 or 5.
Bits 4 and 5 of Configuration Register 5 set the polarity of
the REQ and ACK pins respectively.
A DMA transfer command sets the Port B read/write
direction (see Table 5). The timing diagram for DMA transfers
is shown in Figure 17. The basic DMA transfer starts with REQ
assertion. After 2 to 5 internal clocks, ACK is asserted by the
BiFIFO. ACK will not be asserted if a read is attempted on an
empty A→B FIFO or if a write is attempted on a full B→A FIFO.
If the BiFIFO is in Motorola-style interface mode, R/WB is set
at the same time that ACK is asserted. One internal clock later,
DSB is asserted. If the BiFIFO is in Intel-style interface mode,
either RB or WB is asserted one internal clock after ACK
assertion. These read/write controls stay asserted for 1 or 2
internal clocks, then ACK, DSB, RB and WB are made inactive.
This completes the transfer of one 9-bit word.
On the next rising edge of CLK, REQ is sampled. If REQ
is still asserted, another DMA transfer starts with the assertion
of ACK. Data transfers will continue as long as REQ is
asserted.
Intelligent Reread/Rewrite
Intelligent reread/rewrite is a method the BiFIFO uses to
help assure data integrity. Port B of the BiFIFO has two extra
pointers, the Reread Pointer and the Rewrite Pointer.The
Reread Pointer is associated with the A->B FIFO Read
Pointer, while the Rewrite Pointer is associated with the B->A
FIFO Write Pointer. The Reread Pointer holds the start ad-
dress of a data block in the A->B FIFO RAM, and the Read
Pointer is the current address of the same FIFO RAM array.
By loading the Read Pointer with the value held in the Reread
Pointer (RER asserted), reads will start over at the beginning
of the data block. In order to mark the beginning of a data
block, the Reread Pointer should be loaded with the Read
Pointer value (LDRER asserted) before the first read is
performed on this data block. Figure 6 shows a Reread
operation.
Similarly, the Rewrite Pointer holds the start address of a
data block in the B->A FIFO RAM, while the Write Pointer is
the current address within the RAM array. The operation of the
REW and LDREW is identical to the RER and LDRER dis-
cussed above. Figure 7 shows a Rewrite operation.
For the reread data protection, Bit 2 of Configuration
Register 5 can be set to 1 to prevent the data block from being
overwritten. In this way, the assertion of A->B full flag will occur
when the write pointer meets the reread pointer instead of the
read pointer as in the normal definition. For the rewrite data
protection, Bit 3 of Configuration Register 5 can be set to 1 to
INTERNAL FLAG TRUTH TABLE
Number of Words in FIFO
From
To
Empty Flag
Almost-Empty Flag Almost-Full Flag
Full Flag
0
0
Asserted
Asserted
Not Asserted
Not Asserted
1
n
Not Asserted
Asserted
Not Asserted
Not Asserted
n+1
D – (m + 1)
Not Asserted
Not Asserted
Not Asserted
Not Asserted
D–m
D–1
Not Asserted
Not Asserted
Asserted
Not Asserted
D
D
Not Asserted
Not Asserted
Asserted
Asserted
NOTE:
2668 tbl 15
1. BiFIFO flags must be assigned to external flag pins to be observed. D = FIFO depth (IDT72511 = 512, IDT72521 = 1024), n = Almost-Empty flag
offset, m = Almost-Full flag offset.
Table 11. Internal Flag Truth Table
5.32
12
Share Link: 