IDT7005S/L
HIGH-SPEED 8K x 8 DUAL-PORT STATIC RAM
MILITARY AND COMMERCIAL TEMPERATURE RANGES
TRUTH TABLE II —
ADDRESS BUSY ARBITRATION
Inputs
Outputs
A0L-A12L
CER A0R-A12R BUSYL
(1)
(1)
CEL
X
BUSYR
Function
Normal
X
X
H
L
NO MATCH
MATCH
H
H
H
H
H
Normal
X
MATCH
H
H
Normal
Write Inhibit(3)
L
MATCH
(2)
(2)
NOTES:
2738 tbl 18
1. Pins BUSYL and BUSYR are both outputs when the part is configured as a master. Both are inputs when configured as a slave. BUSYX outputs on the
IDT7005 are push-pull, not open drain outputs. On slaves the BUSYX input internally inhibits writes.
2. 'L' if the inputs to the opposite port were stable prior to the address and enable inputs of this port. 'H' if the inputs to the opposite port became stable after
the address and enable inputs of this port. If tAPS is not met, either BUSYL or BUSYR = Low will result. BUSYL and BUSYR outputs can not be low
simultaneously.
3. Writes to the left port are internally ignored when BUSYL outputs are driving low regardless of actual logic level on the pin. Writes to the right port are
internally ignored when BUSYR outputs are driving low regardless of actual logic level on the pin.
TRUTH TABLE III — EXAMPLE OF SEMAPHORE PROCUREMENT SEQUENCE(1,2)
Functions
D0 - D7 Left
D0 - D7 Right
Status
No Action
1
0
0
1
1
0
1
1
1
0
1
1
1
1
0
0
1
1
0
1
1
1
Semaphore free
Left Port Writes "0" to Semaphore
Right Port Writes "0" to Semaphore
Left Port Writes "1" to Semaphore
Left Port Writes "0" to Semaphore
Right Port Writes "1" to Semaphore
Left Port Writes "1" to Semaphore
Right Port Writes "0" to Semaphore
Right Port Writes "1" to Semaphore
Left Port Writes "0" to Semaphore
Left Port Writes "1" to Semaphore
Left port has semaphore token
No change. Right side has no write access to semaphore
Right port obtains semaphore token
No change. Left port has no write access to semaphore
Left port obtains semaphore token
Semaphore free
Right port has semaphore token
Semaphore free
Left port has semaphore token
Semaphore free
NOTES:
2738 tbl 19
1. This table denotes a sequence of events for only one of the eight semaphores on the IDT7005.
2. There are eight semaphore flags written to via I/O0 and read from all I/O's (I/O0-I/O7). These eight semaphores are addressed by A0 - A2.
FUNCTIONAL DESCRIPTION
theleftportwritestomemorylocation1FFF(HEX)andtoclear
the interrupt flag (INTR), the right port must read the memory
location 1FFF. The message (8 bits) at 1FFE or 1FFF is user-
defined, since it is an addressable SRAM location. If the
interrupt function is not used, address locations 1FFE and
1FFF are not used as mail boxes, but as part of the random
access memory. Refer to Truth Table for the interrupt opera-
tion.
The IDT7005 provides two ports with separate control,
addressandI/Opinsthatpermitindependentaccessforreads
or writes to any location in memory. The IDT7005 has an
automatic power down feature controlled by CE. The CE
controls on-chip power down circuitry that permits the respec-
tive port to go into a standby mode when not selected (CE
high). When a port is enabled, access to the entire memory
array is permitted.
BUSY LOGIC
INTERRUPTS
Busy Logic provides a hardware indication that both ports
of the RAM have accessed the same location at the same
time. It also allows one of the two accesses to proceed and
signalstheothersidethattheRAMis“Busy”. Thebusypincan
thenbeusedtostalltheaccessuntiltheoperationon theother
side is completed. If a write operation has been attempted
from the side that receives a busy indication, the write signal
is gated internally to prevent the write from proceeding.
If the user chooses to use the interrupt function, a memory
location(mailboxormessagecenter)isassignedtoeachport.
Theleftportinterruptflag(INTL)isassertedwhentherightport
writes to memory location 1FFE (HEX), where a write is
defined as CE = R/W= VIL per the Truth Table . The left port
clears the interrupt through access of address location 1FFE
when CE = OE = VIL. For this example, R/W is a "don't care".
Likewise, the right port interrupt flag (INTR) is asserted when
6.06
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