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SN74ABT7819A-10PH データシート(PDF) 7 Page - Texas Instruments |
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SN74ABT7819A-10PH データシート(HTML) 7 Page - Texas Instruments |
7 / 21 page SN74ABT7819A 512 × 18 × 2 CLOCKED BIDIRECTIONAL FIRST-IN, FIRST-OUT MEMORY SCBS756 – MAY 2002 7 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 Terminal Functions (Continued) TERMINAL† I/O DESCRIPTION NAME NO. I/O DESCRIPTION HFA 4 O FIFOA–B half-full flag. HFA is high when FIFOA–B contains 256 or more words and is low when FIFOA–B contains 255 or fewer words. HFA is set low after FIFOA–B is reset. HFB 61 O FIFOB–A half-full flag. HFB is high when FIFOB–A contains 256 or more words and is low when FIFOB–A contains 255 or fewer words. HFB is set low after FIFOB–A is reset. IRA 5 O Port-A input-ready flag. IRA is synchronized to the low-to-high transition of CLKA. When IRA is low, FIFOA–B is full and writes to its array are disabled. IRA is set low during a FIFOA–B reset and is set high on the second low-to-high transition of CLKA after reset. IRB 60 O Port-B input-ready flag. IRB is synchronized to the low-to-high transition of CLKB. When IRB is low, FIFOB–A is full and writes to its array are disabled. IRB is set low during a FIFOB–A reset and is set high on the second low-to-high transition of CLKB after reset. ORA 74 O Port-A output-ready flag. ORA is synchronized to the low-to-high transition of CLKA. When ORA is low, FIFOB–A is empty and reads from its array are disabled. The last valid word remains on the FIFOB–A outputs when ORA is low. Ready data is present for the A0–A17 outputs when ORA is high. ORA is set low during a FIFOB–A reset and goes high on the third low-to-high transition of CLKA after the first word is loaded to an empty FIFOB–A. ORB 71 O Port-B output-ready flag. ORB is synchronized to the low-to-high transition of CLKB. When ORB is low, FIFOA–B is empty and reads from its array are disabled. The last valid word remains on the FIFOA–B outputs when ORB is low. Ready data is present for the B0–B17 outputs when ORB is high. ORB is set low during a FIFOA–B reset and goes high on the third low-to-high transition of CLKB after the first word is loaded to an empty FIFOA–B. PENA 2 I AF/AEA program enable. After FIFOA–B is reset and before a word is written to its array, the binary value on A0–A7 is latched as an AF/AEA offset when PENA is low and CLKA is high. PENB 63 I AF/AEB program enable. After FIFOB–A is reset and before a word is written to its array, the binary value on B0–B7 is latched as an AF/AEB offset when PENB is low and CLKB is high. RENA 75 I Port-A read enable. A high level on RENA enables data to be read from FIFOB–A on the low-to-high transition of CLKA when CSA is low, W/RA is low, and ORA is high. RENB 70 I Port-B read enable. A high level on RENB enables data to be read from FIFOA–B on the low-to-high transition of CLKB when CSB is low, W/RB is low, and ORB is high. RSTA 1 I FIFOA–B reset. To reset FIFOA–B, four low-to-high transitions of CLKA and four low-to-high transitions of CLKB must occur while RSTA is low. This sets HFA low, IRA low, ORB low, and AF/AEA high. RSTB 64 I FIFOB–A reset. To reset FIFOB–A, four low-to-high transitions of CLKA and four low-to-high transitions of CLKB must occur while RSTB is low. This sets HFB low, IRB low, ORA low, and AF/AEB high. WENA 77 I Port-A write enable. A high level on WENA enables data on A0–A17 to be written into FIFOA–B on the low-to-high transition of CLKA when W/RA is high, CSA is low, and IRA is high. WENB 68 I Port-B write enable. A high level on WENB enables data on B0–B17 to be written into FIFOB–A on the low-to-high transition of CLKB when W/RB is high, CSB is low, and IRB is high. W/RA 79 I Port-A write/read select. A high on W/RA enables A0–A17 data to be written to FIFOA–B on a low-to-high transition of CLKA when WENA is high, CSA is low, and IRA is high. A low on W/RA enables data to be read from FIFOB–A on a low-to-high transition of CLKA when RENA is high, CSA is low, and ORA is high. The A0–A17 outputs are in the high-impedance state when W/RA is high. W/RB 66 I Port-B write/read select. A high on W/RB enables B0–B17 data to be written to FIFOB–A on a low-to-high transition of CLKB when WENB is high, CSB is low, and IRB is high. A low on W/RB enables data to be read from FIFOA–B on a low-to-high transition of CLKB when RENB is high, CSB is low, and ORB is high. The B0–B17 outputs are in the high-impedance state when W/RB is high. † Terminal numbers are for the PH package. |
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