在指定UM(易失性内存)保存数据
int um_write(int $um_id, int $offset, int/string $wbuf [, int $wlen = MAX_STRING_LEN])
成功时保存的数据大小,失败时0
<?php
include "/lib/sd_340.php";
$wbuf = "abcde";
$rbuf = "";
um_write(0, 0, $wbuf, 5); // Writing 5 bytes of data to the address 0 of the UM0
um_read(0, 0, $rbuf, 5); // Reading 5 bytes of data from the address 0 of the UM0
hexdump($rbuf); // Outputting the data
?>