UART0 RTC/CTS not working

[gailu]

Hi Experts,
We are interfacing modem (SIM800) with UART0 of ESP-12F. We are getting Rx Overflow in UART Driver when 656 bytes are received from modem. We are trying to solve proble with RTS/CTS and made following connection as RTS/CTS line in UART Driver are GPIO15 and GPIO13

GPIO15 (RTS) ---------------------Modem (CTS)
|
-------R1(10K)-------GND

GPIO13 (CTS) ---------------------Modem (RTS)

If we remove Pull down from GPIO15 then ESP does not boot that is the reason for having 10K->GND on GPIO15

When we tried with this connection setup, AT command does not reach to modem (we have verified that hardware flow control is enabled in modem, also enabled in ESP - uart.h)

How to use RTS/CTS on UART0 with ESP8266 ? Why it is not working?

[Her Mary]

Without CTS/RTS, can the AT command work?