From 1c5d969f46ccd5333f602dfbe2b0a1295650b9b0 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?St=C3=A9phane=20Raimbault?= Date: Wed, 25 Oct 2017 20:35:47 +0200 Subject: [PATCH 1/2] Only set SER_RS485_ENABLED bit of existing RS485 settings Thanks to @JCWren --- src/modbus-rtu.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/src/modbus-rtu.c b/src/modbus-rtu.c index 8d9f386..f2911d6 100644 --- a/src/modbus-rtu.c +++ b/src/modbus-rtu.c @@ -909,9 +909,13 @@ int modbus_rtu_set_serial_mode(modbus_t *ctx, int mode) #if HAVE_DECL_TIOCSRS485 modbus_rtu_t *ctx_rtu = ctx->backend_data; struct serial_rs485 rs485conf; - memset(&rs485conf, 0x0, sizeof(struct serial_rs485)); if (mode == MODBUS_RTU_RS485) { + // Get + if (ioctl(ctx->s, TIOCGRS485, &rs485conf) < 0) { + return -1; + } + // Set rs485conf.flags = SER_RS485_ENABLED; if (ioctl(ctx->s, TIOCSRS485, &rs485conf) < 0) { return -1; @@ -923,6 +927,10 @@ int modbus_rtu_set_serial_mode(modbus_t *ctx, int mode) /* Turn off RS485 mode only if required */ if (ctx_rtu->serial_mode == MODBUS_RTU_RS485) { /* The ioctl call is avoided because it can fail on some RS232 ports */ + if (ioctl(ctx->s, TIOCGRS485, &rs485conf) < 0) { + return -1; + } + rs485conf.flags &= ~SER_RS485_ENABLED; if (ioctl(ctx->s, TIOCSRS485, &rs485conf) < 0) { return -1; } -- 2.21.0