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74ACT715PC 数据表(PDF) 7 Page - Fairchild Semiconductor |
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74ACT715PC 数据表(HTML) 7 Page - Fairchild Semiconductor |
7 / 14 page 7 www.fairchildsemi.com ADDRDEC LOGIC The ADDRDEC logic decodes the current address and generates the enable signal for the appropriate register. The enable values for the registers and counters change on the falling edge of LOAD. Two types of ADDRDEC logic is enabled by 2 pair of addresses, Addresses 22 or 54 (Vectored Restart logic) and Addresses 23 or 55 (Vectored Clear logic). Loading these addresses will enable the appropriate logic and put the part into either a Restart (all counter registers are reinitialized with preprogrammed data) or Clear (all registers are cleared to zero) state. Reloading the same ADDRDEC address will not cause any change in the state of the part. The outputs during these states are frozen and the internal CLOCK is disabled. Clocking the part during a Vectored Restart or Vectored Clear state will have no effect on the part. To resume oper- ation in the new state, or disable the Vectored Restart or Vectored Clear state, another non-ADDRDEC address must be loaded. Operation will begin in the new state on the rising edge of the non-ADDRDEC load pulse. It is rec- ommended that an unused address be loaded following an ADDRDEC operation to prevent data registers from acci- dentally being corrupted. The following Addresses are used by the device. Address 0 Status Register REG0 Address 1–18Data Registers REG1–REG18 Address 19–21Unused Address 22/54Restart Vector (Restarts Device) Address 23/55Clear Vector (Zeros All Registers) Address 24–31Unused Address 32–50Register Scan Addresses Address 51–53Counter Scan Addresses Address 56–63Unused At any given time only one register at most is selected. It is possible to have no registers selected. VECTORED RESTART ADDRESS The function of addresses 22 (16H) or 54 (36H) are similar to that of the CLR pin except that the preprogramming of the registers is not affected. It is recommended but not required that this address is read after the initial device configuration load sequence. A 1 on the ADDRDATA pin (Auto Addressing Mode) will not cause this address to automatically increment. The address will loop back onto itself regardless of the state of ADDRDATA unless the address on the Data inputs has been changed with ADDRDATA at 0. VECTORED CLEAR ADDRESS Addresses 23 (17H) or 55 (37H) is used to clear all regis- ters to zero simultaneously. This function may be desirable to use prior to loading new data into the Data or Status Registers. This address is read into the device in a similar fashion as all of the other registers. A 1 on the ADDRDATA pin (Auto Addressing Mode) will not cause this address to automatically increment. The address will loop back onto itself regardless of the state of ADDRDATA unless the address on the Data inputs has been changed with ADDRDATA at 0. FIGURE 4. ADDRDEC Timing GEN LOCKING The ACT715 and ACT715-R is designed for master SYNC and BLANK signal generation. However, the devices can be synchronized (slaved) to an external timing signal in a limited sense. Using Vectored Restart, the user can reset the counting sequence to a given location, the beginning, at a given time, the rising edge of the LOAD that removes Vector Restart. At this time the next CLOCK pulse will be CLOCK 1 and the count will restart at the beginning of the first odd line. Preconditioning the part during normal operation, before the desired synchronizing pulse, is necessary. However, since LOAD and CLOCK are asynchronous and indepen- dent, this is possible without interruption or data and perfor- mance corruption. If the defaulted 14.31818 MHz RS-170 values are being used, preconditioning and restarting can be minimized by using the CLEAR pulse instead of the Vectored Restart operation. The ACT715-R is better suited for this application because it eliminates the need to pro- gram a 1 into Bit 10 of the Status Register to enable the CLOCK. Gen Locking to another count location other than the very beginning or separate horizontal/vertical resetting is not possible with the ACT715 nor the ACT715-R. SCAN MODE LOGIC A scan mode is available in the ACT715 that allows the user to non-destructively verify the contents of the regis- ters. Scan mode is invoked through reading a scan address into the address register. The scan address of a given register is defined by the Data register address + 32. The internal Clocking signal is disabled when a scan address is read. Disabling the clock freezes the device in it's present state. Data can then be serially scanned out of the data registers through the ODD/EVEN Pin. The LSB will be scanned out first. Since each register is 12 bits wide, completely scanning out data of the addressed register will require 12 CLOCK pulses. More than 12 CLOCK pulses on the same register will only cause the MSB to repeat on the output. Re-scanning the same register will require that reg- ister to be reloaded. The value of the two horizontal counters and 1 vertical counter can also be scanned out by using address numbers 51–53. Note that before the part will scan out the data, the LOAD signal must be brought back HIGH. Normal device operation can be resumed by loading in a non-scan address. As the scanning of the registers is a non-destructive scan, the device will resume correct opera- tion from the point at which it was halted. |
类似零件编号 - 74ACT715PC |
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类似说明 - 74ACT715PC |
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