uart.write(bytes(cframe))改为uart.write(cframe)

使用usb-ttl与ESP32UART硬件流控制正常，接usb-ttl换为OPENMV时出现问题，去掉CTS RTS tcp上位机可接收到jpge，jpge有数据丢失，未达到UART硬件流控制效果。参考中文文档未解决，能否提供一份一份openmv的UART硬件流控制的dome代码？谢谢。
PS:使用IDE2.9.0,固件为4.3.0，UART3(P4 P5) CTS P2 RTS P1。

import sensor, image, time
import time
from machine  import UART
import utime

sensor.reset()                      # Reset and initialize the sensor.
sensor.set_pixformat(sensor.RGB565) # Set pixel format to RGB565 (or GRAYSCALE)
sensor.set_framesize(sensor.VGA)   # Set frame size to QVGA (320x240)
sensor.skip_frames(time = 2000)     # Wait for settings take effect.

uart = UART(3, 5000000,flow=UART.CTS,timtout=1000,timeout_char=1000,read_buf_len=5120) # 使用给定参数初始化


#uart = UART(3, 5000000,timeout_char=1000)
#uart.init(5000000,flow=UART.CTS,timeout_char=1000,read_buf_len=5120) # 使用给定参数初始化
#flow=UART.RTS|UART.CTS
while(True):

    frame = sensor.snapshot()
    cframe = frame.compress(quality=15)#compressed
    uart.write(bytes(cframe))

Traceback (most recent call last):
File "", line 9, in
AttributeError: type object 'Pin' has no attribute 'PULL_UP'
Current datetime1: 2019-02-18 12:02:14
Unique ID: 2969 65f8 91d2 2a17
MicroPython v1.9.3 on 2019-04-26; mimxrt1050-eMicroPython v1.9.3 onType "help()" for more information.