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CYDM064B16 Datasheet(PDF) 7 Page - Cypress Semiconductor |
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CYDM064B16 Datasheet(HTML) 7 Page - Cypress Semiconductor |
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7 / 27 page  CYDM064B16 CYDM128B16 CYDM256B16 Document #: 001-00217 Rev. *H Page 7 of 27 Input Read Register The Input Read Register (IRR) captures the status of two external input devices that are connected to the Input Read pins. The contents of the IRR read from address x0000 from either port. During reads from the IRR, DQ0 and DQ1 are valid bits and DQ<15:2> are don’t care. Writes to address x0000 are not allowed from either port. Address x0000 is not available for standard memory accesses when SFEN = VIL. When SFEN = VIH, address x0000 is available for memory accesses. The inputs are 1.8V/2.5V LVCMOS or 3.0V LVTTL, depending on the core voltage supply (VCC). Refer to Table 4 on page 9 for Input Read Register operation. IRR is not available in the CYDM256B16, because the IRR pins are used as extra address pins A13L and A13R. Output Drive Register The Output Drive Register (ODR) determines the state of up to five external binary state devices by providing a path to VSS for the external circuit. These outputs are Open Drain. The five external devices can operate at different voltages (1.5V ≤ V DDIO ≤ 3.5V) but the combined current cannot exceed 40 mA (8 mA max for each external device). The status of the ODR bits are set using standard write accesses from either port to address x0001 with a “1” corresponding to on and “0” corresponding to off. The status of the ODR bits can be read with a standard read access to address x0001. When SFEN = VIL, the ODR is active and address x0001 is not available for memory accesses. When SFEN = VIH, the ODR is inactive and address x0001 can be used for standard accesses. During reads and writes to ODR DQ<4:0> are valid and DQ<15:5> are don’t care. Refer to Table 5 on page 9 for Output Drive Register operation. Semaphore Operation The CYDM256B16, CYDM128B16, and CYDM064B16 provide eight semaphore latches, which are separate from the dual-port memory locations. Semaphores are used to reserve resources that are shared between the two ports. The state of the semaphore indicates that a resource is in use. For example, if the left port wants to request a given resource, it sets a latch by writing a zero to a semaphore location. The left port then verifies its success in setting the latch by reading it. After writing to the semaphore, SEM or OE must be deasserted for tSOP before attempting to read the semaphore. The semaphore value is available tSWRD + tDOE after the rising edge of the semaphore write. If the left port is successful (reads a zero), it assumes control of the shared resource. Otherwise (reads a one), it assumes the right port has control and continues to poll the semaphore. When the right side has relinquished control of the semaphore (by writing a one), the left side succeeds in gaining control of the semaphore. If the left side no longer requires the semaphore, a one is written to cancel its request. Semaphores are accessed by asserting SEM LOW. The SEM pin functions as a chip select for the semaphore latches (CE must remain HIGH during SEM LOW). A0–2 represents the semaphore address. OE and R/W are used in the same manner as a normal memory access. When writing or reading a semaphore, the other address pins have no effect. When writing to the semaphore, only IO0 is used. If a zero is written to the left port of an available semaphore, a one appears at the same semaphore address on the right port. That semaphore can now only be modified by the side showing zero (the left port in this case). If the left port now relinquishes control by writing a one to the semaphore, the semaphore is set to one for both sides. However, if the right port requests the semaphore (written a zero) while the left port has control, the right port immediately owns the semaphore as soon as the left port releases it. Table 6 on page 9 shows sample semaphore operations. When reading a semaphore, all sixteen data lines output the semaphore value. The read value is latched in an output register to prevent the semaphore from changing state during a write from the other port. If both ports attempt to access the semaphore within tSPS of each other, the semaphore is definitely obtained by one side or the other, but there is no guarantee which side controls the semaphore. On power up, both ports must write “1” to all eight semaphores. Architecture The CYDM256B16, CYDM128B16, and CYDM064B16 consist of an array of 4K, 8K, or 16K words of 16 dual-port RAM cells, I/O and address lines, and control signals (CE, OE, R/W). These control pins permit independent access for reads or writes to any location in memory. To handle simultaneous writes or reads to the same location, a BUSY pin is provided on each port. Two Interrupt (INT) pins can be used for port-to-port communication. Two Semaphore (SEM) control pins are used to allocate shared resources. With the M/S pin, the devices can function as a master (BUSY pins are outputs) or as a slave (BUSY pins are inputs). The devices also have an automatic power down feature controlled by CE. Each port is provided with its own output enable control (OE), which allows data to be read from the device. [+] Feedback |
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