AT89C2051-24PU 的U的意义是什么？

AT89C2051-24PU
ATMEL单片机 晶振最高支持24M，塑料双列直插DIP封装，温度-40至+85℃，U指的是无铅元件

2008B   SOP 07+ ATMEL 370 Stock
2010B-MY   DIP16 07+ ATMEL 2688 Stock
211B-MFPG3Y   SOIC16 07+ ATMEL 20000 Stock
211B-MFPY   SO16 07+ ATMEL 44800 Stock
24C01A-10PU-2.7   DIP 07+ ATMEL 20000 Stock
24C01A-10SU-2.7   SOP 07+ ATMEL 20000 Stock
24C01A-10TI-2.7   TSOP 07+ ATMEL 12000 Stock
24C02B-10PU-2.7   DIP 07+ ATMEL 20000 Stock
24C02BN-10SU-1.8   SOP 07+ ATMEL 20000 Stock
24C02BN-10SU-2.7   SOP 07+ ATMEL 20000 Stock
24C02N-10SU-2.7   SOP 07+ ATMEL 20000 Stock
24C04A-10PU-2.7   DIP 07+ ATMEL 20000 Stock
24C04AN-10SU-1.8   SOP 07+ ATMEL 20000 Stock
24C04AN-10SU-2.7   SOP 07+ ATMEL 20000 Stock
24C04N-10SU-1.8   SOP 07+ ATMEL 20000 Stock
24C08AN-10SU-2.7   SOP 07+ ATMEL 20000 Stock
24C1024W-10SI-2.7   SOP 07+ ATMEL 3600 Stock
24C128B-TH-T   TSSOP8 07+ ATMEL 5000 Stock
24C128N-10SI-2.7   SOP 07+ ATMEL 11400 Stock
24C16A-10PU-2.7   DIP 07+ ATMEL 20000 Stock
24C16A-10TI-1.8   TSOP 07+ ATMEL 20000 Stock
24C16AN-10SU-2.7   SOP 07+ ATMEL 20000 Stock
24C256-10PI-2.7   DIP 07+ ATMEL 296 Stock
24C256-10TI-2.7   TSOP 07+ ATMEL 9000 Stock
24C256BN-SH-T   SOIC-8 07+ ATMEL 52000 Stock
24C256B-PU   DIP8 07+ ATMEL 3000 Stock
24C256N-10SU-2.7   SOP 07+ ATMEL 3000 Stock
24C32A-10PU-2.7   DIP 07+ ATMEL 20000 Stock
24C32AN-10SU-2.7   SOP 07+ ATMEL 20000 Stock
24C32CN-SH-T   SO-8 07+ ATMEL 100000 Stock
24C512BN-SH25-T   SO-8 07+ ATMEL 16000 Stock
24C512B-PU25   DIP8 07+ ATMEL 10000 Stock
24C512N-10SU-2.7   SOP 07+ ATMEL 6700 Stock
24C512W-10SI-2.7   SOP 07+ ATMEL 8000 Stock
24C64AN-10SU-2.7   SOP 07+ ATMEL 20000 Stock
25080AN-10SU-2.7   SOP 07+ ATMEL 30000 Stock
25640A-10PU-2.7   SO-8 07+ ATMEL 2800 Stock
25640AN-10SU-2.7   SOP 07+ ATMEL 4000 Stock
27BV512-70JU   PLCC32 07+ ATMEL 50000 Stock
27C512R-70JU   PLCC32 07+ ATMEL 4000 Stock
27CO40-70PU   DIP32 07+ ATMEL 980 Stock
28BV64B-20SU   SOIC28 07+ ATMEL 1000 Stock
28C16-15PI   PLCC 07+ ATMEL 3470 Stock
28C256-15JU   PLCC32 07+ ATMEL 832 Stock
28C256-15JU   PICC32 07+ ATMEL 832 Stock
29C010A-7OJU   PLCC32 07+ ATMEL 2000 Stock
45DB041D-SU   SOIC8 07+ ATMEL 50000 Stock
45DB081B-TU   DIP 07+ ATMEL 1513 Stock
45DB11B-SU   SOIC-8 07+ ATMEL 10000 Stock
45DB161B-TU   TSOP 07+ ATMEL 4200 Stock
45DB161D-TU   TSOP 07+ ATMEL 12780 Stock
45DB642D-CNU   CASON8 07+ ATMEL 5000 Stock
487ECSA+T   NSO8 07+ MAXIM 2300 Stock
489CPD+   DIP14 07+ MAXIM 539 Stock
49BV162A-70TI   TSOP 07+ ATMEL 5576 Stock
49BV163D-70TU   TSOP 07+ ATMEL 5940 Stock
8212CPA7   DIP8 07+ MAXIM 145 Stock
86RF211SAHW-R   TQFP48 07+ ATMEL 20000 Stock
87C51RB2-3CSUM   DIP14 07+ ATMEL 6696 Stock
88SCO104C-SU   SOIC8 07+ ATMEL 20000 Stock
88SCO808C-SU   SOIC8 07+ ATMEL 4000 Stock
89C2051-12PU   DIP20 07+ ATMEL 10008 Stock
89C2051-12SU   SOIC20 07+ ATMEL 3697 Stock
89C51AC2-SLSUM   TSOP 07+ ATMEL 6800 Stock
89C51ED2-RLTUM   PLCC 07+ ATMEL 891 Stock
89C51RC2-SLSIM   QFP 07+ ATMEL 470 Stock
89C51RD2-RLTUM   VQFP44 07+ ATMEL 2400 Stock
89C51RD2-SLSIM   PLCC 07+ ATMEL 520 Stock
89S2051-24PU   DIP20 07+ ATMEL 2016 Stock
89S4051-24SU   SOIC20 07+ ATMEL 349 Stock
91SAM7A3-AU   LQFP100 07+ ATMEL 1620 Stock
93C46D-PU   DIP8 07+ ATMEL 50000 Stock
93C46D-TH-T   TSOP8 07+ ATMEL 100000 Stock
1502AS-10JC44   PLCC 07+ ATMEL 3248 Stock
1508AS-15QC100   PLCC 07+ ATMEL 1080 Stock
16V8B-10JC   QFP 07+ ATMEL 1410 Stock
MAX487ECSA+T   NSO8 07+ MAXIM 2300 Stock
MAX489CPD+   DIP14 07+ MAXIM 539 Stock
MAX8212CPA7   DIP8 07+ MAXIM 145 Stock
MEGA128L-8AU   PLCC 07+ ATMEL 2365 Stock
MEGA128L-8MU   MLF64 07+ ATMEL 3640 Stock
MEGA16-16AI   QFP 07+ ATMEL 1200 Stock
MEGA16-16AU   TQFP44 07+ ATMEL 20000 Stock
MEGA164P-20AU   TQFP44 07+ ATMEL 2550 Stock
MEGA168-20PU   DIP28 07+ ATMEL 3010 Stock
MEGA168V-10MU   MLF32 07+ ATMEL 45570 Stock
MEGA16L-8AU   TQFP44 07+ ATMEL 20000 Stock
MEGA2560-16AU   QFP 07+ ATMEL 1600 Stock
MEGA2561V-8AU   TQFP64 07+ ATMEL 450 Stock
MEGA32L-8AU   QFP 07+ ATMEL 210 Stock
MEGA48-20AU   TQFP32 07+ ATMEL 20000 Stock
MEGA48V-10AU   TQFP32 07+ ATMEL 33750 Stock
MEGA48V-10PU   DIP28 07+ ATMEL 20000 Stock
MEGA644P-20AU   TQFP44 07+ ATMEL 1920 Stock
MEGA64L-8AU   TQFP64 07+ ATMEL 5176 Stock
MEGA8-16AU   QFP 07+ ATMEL 1320 Stock
MEGA8-16PU   DIP28 07+ ATMEL 5013 Stock
MEGA8515-16JU   PLCC44 07+ ATMEL 2160 Stock
MEGA8535L-8AU   TQFP44 07+ ATMEL 25600 Stock
MEGA8535L-8PU   DIP40 07+ ATMEL 5000 Stock
MEGA88-20AU   TQFP32 07+ ATMEL 20000 Stock
MEGA88V-10AU   TQFP32 07+ ATMEL 20000 Stock
MEGA8L-8AU   TQFP32 07+ ATMEL 49000 Stock
R2406PNSG   QFP 07+ ATMEL 1000 Stock
TINY12-8SI   SOP 07+ ATMEL 290 Stock
TINY13V-10SU   SOIC8 07+ ATMEL 86304 Stock
TINY13V-1OPU   DIP8 07+ ATMEL 4000 Stock
TINY2313-20PU   DIP20 07+ ATMEL 4274 Stock
TINY2313-20SU   SOIC20 07+ ATMEL 5032 Stock
TINY2313V-10SU   SOP 07+ ATMEL 9500 Stock
TINY24V-10SSU   SOP 07+ ATMEL 5960 Stock
TINY26L-16SU   SOIC20 07+ ATMEL 9374 Stock
TINY26L-8MU   MLF32 07+ ATMEL 490 Stock
TINY26L-8SU   SOIC20 07+ ATMEL 20054 Stock
TINY461V-10SU   SOIC20 07+ ATMEL 5032 Stock
TINY861-20MU   MLF32 07+ ATMEL 2009 Stock
TINY861-20SU   SOIC20 07+ ATMEL 2035 Stock
U2008B   SOP 07+ ATMEL 370 Stock
U2010B-MY   DIP16 07+ ATMEL 2688 Stock
U211B-MFPG3Y   SOIC16 07+ ATMEL 20000 Stock
U211B-MFPY   SO16 07+ ATMEL 44800 Stock