"""Program 4-2: Loopback test. Observe whether the receive buffer is empty.
           Put a jumper between the GP21 pin and the GP20 pin.
"""

import time
from machine import UART, Pin

uart1 = UART(1, baudrate = 9600, rx = Pin(21), tx = Pin(20))
m = uart1.write("ABCDEFGHIJKLMNOPQRSTUVWXYZ")
n = uart1.any()
time.sleep_ms(10)
p = uart1.any()
time.sleep_ms(20)
q = uart1.any()

print (m, n, p, q)