diff --git a/hardware/serial-dmm/api.c b/hardware/serial-dmm/api.c
index 136d2a7c..12396901 100644
--- a/hardware/serial-dmm/api.c
+++ b/hardware/serial-dmm/api.c
@@ -78,112 +78,112 @@ SR_PRIV struct sr_dev_driver tenma_72_7750_ser_driver_info;
 SR_PRIV struct dmm_info dmms[] = {
 	{
 		"BBC Goertz Metrawatt", "M2110", "1200/7n2", 1200,
-		BBCGM_M2110_PACKET_SIZE, NULL,
+		BBCGM_M2110_PACKET_SIZE, 0, 0, NULL,
 		sr_m2110_packet_valid, sr_m2110_parse,
 		NULL,
 		&bbcgm_m2110_driver_info, receive_data_BBCGM_M2110,
 	},
 	{
 		"Digitek", "DT4000ZC", "2400/8n1/dtr=1", 2400,
-		FS9721_PACKET_SIZE, NULL,
+		FS9721_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9721_packet_valid, sr_fs9721_parse,
 		sr_fs9721_10_temp_c,
 		&digitek_dt4000zc_driver_info, receive_data_DIGITEK_DT4000ZC,
 	},
 	{
 		"TekPower", "TP4000ZC", "2400/8n1/dtr=1", 2400,
-		FS9721_PACKET_SIZE, NULL,
+		FS9721_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9721_packet_valid, sr_fs9721_parse,
 		sr_fs9721_10_temp_c,
 		&tekpower_tp4000zc_driver_info, receive_data_TEKPOWER_TP4000ZC,
 	},
 	{
 		"Metex", "ME-31", "600/7n2/rts=0/dtr=1", 600,
-		METEX14_PACKET_SIZE, sr_metex14_packet_request,
+		METEX14_PACKET_SIZE, 0, 0, sr_metex14_packet_request,
 		sr_metex14_packet_valid, sr_metex14_parse,
 		NULL,
 		&metex_me31_driver_info, receive_data_METEX_ME31,
 	},
 	{
 		"Peaktech", "3410", "600/7n2/rts=0/dtr=1", 600,
-		METEX14_PACKET_SIZE, sr_metex14_packet_request,
+		METEX14_PACKET_SIZE, 0, 0, sr_metex14_packet_request,
 		sr_metex14_packet_valid, sr_metex14_parse,
 		NULL,
 		&peaktech_3410_driver_info, receive_data_PEAKTECH_3410,
 	},
 	{
 		"MASTECH", "MAS345", "600/7n2/rts=0/dtr=1", 600,
-		METEX14_PACKET_SIZE, sr_metex14_packet_request,
+		METEX14_PACKET_SIZE, 0, 0, sr_metex14_packet_request,
 		sr_metex14_packet_valid, sr_metex14_parse,
 		NULL,
 		&mastech_mas345_driver_info, receive_data_MASTECH_MAS345,
 	},
 	{
 		"V&A", "VA18B", "2400/8n1", 2400,
-		FS9721_PACKET_SIZE, NULL,
+		FS9721_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9721_packet_valid, sr_fs9721_parse,
 		sr_fs9721_01_temp_c,
 		&va_va18b_driver_info, receive_data_VA_VA18B,
 	},
 	{
 		"V&A", "VA40B", "2400/8n1", 2400,
-		FS9721_PACKET_SIZE, NULL,
+		FS9721_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9721_packet_valid, sr_fs9721_parse,
 		sr_fs9721_max_c_min,
 		&va_va40b_driver_info, receive_data_VA_VA40B,
 	},
 	{
 		"Metex", "M-3640D", "1200/7n2/rts=0/dtr=1", 1200,
-		METEX14_PACKET_SIZE, sr_metex14_packet_request,
+		METEX14_PACKET_SIZE, 0, 0, sr_metex14_packet_request,
 		sr_metex14_packet_valid, sr_metex14_parse,
 		NULL,
 		&metex_m3640d_driver_info, receive_data_METEX_M3640D,
 	},
 	{
 		"Metex", "M-4650CR", "1200/7n2/rts=0/dtr=1", 1200,
-		METEX14_PACKET_SIZE, sr_metex14_packet_request,
+		METEX14_PACKET_SIZE, 0, 0, sr_metex14_packet_request,
 		sr_metex14_packet_valid, sr_metex14_parse,
 		NULL,
 		&metex_m4650cr_driver_info, receive_data_METEX_M4650CR,
 	},
 	{
 		"PeakTech", "4370", "1200/7n2/rts=0/dtr=1", 1200,
-		METEX14_PACKET_SIZE, sr_metex14_packet_request,
+		METEX14_PACKET_SIZE, 0, 0, sr_metex14_packet_request,
 		sr_metex14_packet_valid, sr_metex14_parse,
 		NULL,
 		&peaktech_4370_driver_info, receive_data_PEAKTECH_4370,
 	},
 	{
 		"PCE", "PCE-DM32", "2400/8n1", 2400,
-		FS9721_PACKET_SIZE, NULL,
+		FS9721_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9721_packet_valid, sr_fs9721_parse,
 		sr_fs9721_01_10_temp_f_c,
 		&pce_pce_dm32_driver_info, receive_data_PCE_PCE_DM32,
 	},
 	{
 		"RadioShack", "22-168", "1200/7n2/rts=0/dtr=1", 1200,
-		METEX14_PACKET_SIZE, sr_metex14_packet_request,
+		METEX14_PACKET_SIZE, 0, 0, sr_metex14_packet_request,
 		sr_metex14_packet_valid, sr_metex14_parse,
 		NULL,
 		&radioshack_22_168_driver_info, receive_data_RADIOSHACK_22_168,
 	},
 	{
 		"RadioShack", "22-805", "600/7n2/rts=0/dtr=1", 600,
-		METEX14_PACKET_SIZE, sr_metex14_packet_request,
+		METEX14_PACKET_SIZE, 0, 0, sr_metex14_packet_request,
 		sr_metex14_packet_valid, sr_metex14_parse,
 		NULL,
 		&radioshack_22_805_driver_info, receive_data_RADIOSHACK_22_805,
 	},
 	{
 		"RadioShack", "22-812", "4800/8n1/rts=0/dtr=1", 4800,
-		RS9LCD_PACKET_SIZE, NULL,
+		RS9LCD_PACKET_SIZE, 0, 0, NULL,
 		sr_rs9lcd_packet_valid, sr_rs9lcd_parse,
 		NULL,
 		&radioshack_22_812_driver_info, receive_data_RADIOSHACK_22_812,
 	},
 	{
 		"Tecpel", "DMM-8061 (UT-D02 cable)", "2400/8n1/rts=0/dtr=1",
-		2400, FS9721_PACKET_SIZE, NULL,
+		2400, FS9721_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9721_packet_valid, sr_fs9721_parse,
 		sr_fs9721_00_temp_c,
 		&tecpel_dmm_8061_ser_driver_info,
@@ -191,35 +191,35 @@ SR_PRIV struct dmm_info dmms[] = {
 	},
 	{
 		"Voltcraft", "M-3650CR", "1200/7n2/rts=0/dtr=1", 1200,
-		METEX14_PACKET_SIZE, sr_metex14_packet_request,
+		METEX14_PACKET_SIZE, 150, 20, sr_metex14_packet_request,
 		sr_metex14_packet_valid, sr_metex14_parse,
 		NULL,
 		&voltcraft_m3650cr_driver_info, receive_data_VOLTCRAFT_M3650CR,
 	},
 	{
 		"Voltcraft", "M-3650D", "1200/7n2/rts=0/dtr=1", 1200,
-		METEX14_PACKET_SIZE, sr_metex14_packet_request,
+		METEX14_PACKET_SIZE, 0, 0, sr_metex14_packet_request,
 		sr_metex14_packet_valid, sr_metex14_parse,
 		NULL,
 		&voltcraft_m3650d_driver_info, receive_data_VOLTCRAFT_M3650D,
 	},
 	{
 		"Voltcraft", "M-4650CR", "1200/7n2/rts=0/dtr=1", 1200,
-		METEX14_PACKET_SIZE, sr_metex14_packet_request,
+		METEX14_PACKET_SIZE, 0, 0, sr_metex14_packet_request,
 		sr_metex14_packet_valid, sr_metex14_parse,
 		NULL,
 		&voltcraft_m4650cr_driver_info, receive_data_VOLTCRAFT_M4650CR,
 	},
 	{
 		"Voltcraft", "ME-42", "600/7n2/rts=0/dtr=1", 600,
-		METEX14_PACKET_SIZE, sr_metex14_packet_request,
+		METEX14_PACKET_SIZE, 250, 60, sr_metex14_packet_request,
 		sr_metex14_packet_valid, sr_metex14_parse,
 		NULL,
 		&voltcraft_me42_driver_info, receive_data_VOLTCRAFT_ME42,
 	},
 	{
 		"Voltcraft", "VC-820 (UT-D02 cable)", "2400/8n1/rts=0/dtr=1",
-		2400, FS9721_PACKET_SIZE, NULL,
+		2400, FS9721_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9721_packet_valid, sr_fs9721_parse,
 		NULL,
 		&voltcraft_vc820_ser_driver_info,
@@ -232,7 +232,7 @@ SR_PRIV struct dmm_info dmms[] = {
 		 * bit "z1" to indicate "diode mode" and "voltage".
 		 */
 		"Voltcraft", "VC-830 (UT-D02 cable)", "2400/8n1/rts=0/dtr=1",
-		2400, FS9922_PACKET_SIZE, NULL,
+		2400, FS9922_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9922_packet_valid, sr_fs9922_parse,
 		&sr_fs9922_z1_diode,
 		&voltcraft_vc830_ser_driver_info,
@@ -240,7 +240,7 @@ SR_PRIV struct dmm_info dmms[] = {
 	},
 	{
 		"Voltcraft", "VC-840 (UT-D02 cable)", "2400/8n1/rts=0/dtr=1",
-		2400, FS9721_PACKET_SIZE, NULL,
+		2400, FS9721_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9721_packet_valid, sr_fs9721_parse,
 		sr_fs9721_00_temp_c,
 		&voltcraft_vc840_ser_driver_info,
@@ -248,7 +248,7 @@ SR_PRIV struct dmm_info dmms[] = {
 	},
 	{
 		"UNI-T", "UT60A (UT-D02 cable)", "2400/8n1/rts=0/dtr=1",
-		2400, FS9721_PACKET_SIZE, NULL,
+		2400, FS9721_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9721_packet_valid, sr_fs9721_parse,
 		NULL,
 		&uni_t_ut60a_ser_driver_info,
@@ -256,7 +256,7 @@ SR_PRIV struct dmm_info dmms[] = {
 	},
 	{
 		"UNI-T", "UT60E (UT-D02 cable)", "2400/8n1/rts=0/dtr=1",
-		2400, FS9721_PACKET_SIZE, NULL,
+		2400, FS9721_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9721_packet_valid, sr_fs9721_parse,
 		sr_fs9721_00_temp_c,
 		&uni_t_ut60e_ser_driver_info,
@@ -265,47 +265,47 @@ SR_PRIV struct dmm_info dmms[] = {
 	{
 		/* Note: ES51986 baudrate is actually 19230! */
 		"UNI-T", "UT60G (UT-D02 cable)", "19200/7o1/rts=0/dtr=1",
-		19200, ES519XX_11B_PACKET_SIZE, NULL,
+		19200, ES519XX_11B_PACKET_SIZE, 0, 0, NULL,
 		sr_es519xx_19200_11b_packet_valid, sr_es519xx_19200_11b_parse,
 		NULL,
 		&uni_t_ut60g_ser_driver_info, receive_data_UNI_T_UT60G_SER,
 	},
 	{
 		"UNI-T", "UT61B (UT-D02 cable)", "2400/8n1/rts=0/dtr=1",
-		2400, FS9922_PACKET_SIZE, NULL,
+		2400, FS9922_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9922_packet_valid, sr_fs9922_parse, NULL,
 		&uni_t_ut61b_ser_driver_info, receive_data_UNI_T_UT61B_SER,
 	},
 	{
 		"UNI-T", "UT61C (UT-D02 cable)", "2400/8n1/rts=0/dtr=1",
-		2400, FS9922_PACKET_SIZE, NULL,
+		2400, FS9922_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9922_packet_valid, sr_fs9922_parse, NULL,
 		&uni_t_ut61c_ser_driver_info, receive_data_UNI_T_UT61C_SER,
 	},
 	{
 		"UNI-T", "UT61D (UT-D02 cable)", "2400/8n1/rts=0/dtr=1",
-		2400, FS9922_PACKET_SIZE, NULL,
+		2400, FS9922_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9922_packet_valid, sr_fs9922_parse, NULL,
 		&uni_t_ut61d_ser_driver_info, receive_data_UNI_T_UT61D_SER,
 	},
 	{
 		/* Note: ES51922 baudrate is actually 19230! */
 		"UNI-T", "UT61E (UT-D02 cable)", "19200/7o1/rts=0/dtr=1",
-		19200, ES519XX_14B_PACKET_SIZE, NULL,
+		19200, ES519XX_14B_PACKET_SIZE, 0, 0, NULL,
 		sr_es519xx_19200_14b_packet_valid, sr_es519xx_19200_14b_parse,
 		NULL,
 		&uni_t_ut61e_ser_driver_info, receive_data_UNI_T_UT61E_SER,
 	},
 	{
 		"ISO-TECH", "IDM103N", "2400/7o1/rts=0/dtr=1",
-		2400, ES519XX_11B_PACKET_SIZE, NULL,
+		2400, ES519XX_11B_PACKET_SIZE, 0, 0, NULL,
 		sr_es519xx_2400_11b_packet_valid, sr_es519xx_2400_11b_parse,
 		NULL,
 		&iso_tech_idm103n_driver_info, receive_data_ISO_TECH_IDM103N,
 	},
 	{
 		"Tenma", "72-7745 (UT-D02 cable)", "2400/8n1/rts=0/dtr=1",
-		2400, FS9721_PACKET_SIZE, NULL,
+		2400, FS9721_PACKET_SIZE, 0, 0, NULL,
 		sr_fs9721_packet_valid, sr_fs9721_parse,
 		sr_fs9721_00_temp_c,
 		&tenma_72_7745_ser_driver_info, receive_data_TENMA_72_7745_SER,
@@ -313,7 +313,7 @@ SR_PRIV struct dmm_info dmms[] = {
 	{
 		/* Note: ES51986 baudrate is actually 19230! */
 		"Tenma", "72-7750 (UT-D02 cable)", "19200/7o1/rts=0/dtr=1",
-		19200, ES519XX_11B_PACKET_SIZE, NULL,
+		19200, ES519XX_11B_PACKET_SIZE, 0, 0, NULL,
 		sr_es519xx_19200_11b_packet_valid, sr_es519xx_19200_11b_parse,
 		NULL,
 		&tenma_72_7750_ser_driver_info, receive_data_TENMA_72_7750_SER,
diff --git a/hardware/serial-dmm/protocol.c b/hardware/serial-dmm/protocol.c
index 36e69444..0b2472fb 100644
--- a/hardware/serial-dmm/protocol.c
+++ b/hardware/serial-dmm/protocol.c
@@ -68,6 +68,37 @@ static void handle_packet(const uint8_t *buf, struct sr_dev_inst *sdi,
 	}
 }
 
+/** Request packet, if required. */
+SR_PRIV int req_packet(struct sr_dev_inst *sdi, int dmm)
+{
+	struct dev_context *devc;
+	struct sr_serial_dev_inst *serial;
+	int ret;
+
+	if (!dmms[dmm].packet_request)
+		return SR_OK;
+
+	devc = sdi->priv;
+	serial = sdi->conn;
+
+	if (devc->req_next_at && (devc->req_next_at > g_get_monotonic_time())) {
+		sr_spew("Not requesting new packet yet, %" PRIi64 " ms left.",
+			((devc->req_next_at - g_get_monotonic_time()) / 1000));
+		return SR_OK;
+	}
+
+	ret = dmms[dmm].packet_request(serial);
+	if (ret < 0) {
+		sr_err("Failed to request packet: %d.", ret);
+		return ret;
+	}
+
+	if (dmms[dmm].req_timeout_ms)
+		devc->req_next_at = g_get_monotonic_time() + (dmms[dmm].req_timeout_ms * 1000);
+
+	return SR_OK;
+}
+
 static void handle_new_data(struct sr_dev_inst *sdi, int dmm, void *info)
 {
 	struct dev_context *devc;
@@ -93,6 +124,14 @@ static void handle_new_data(struct sr_dev_inst *sdi, int dmm, void *info)
 		if (dmms[dmm].packet_valid(devc->buf + offset)) {
 			handle_packet(devc->buf + offset, sdi, dmm, info);
 			offset += dmms[dmm].packet_size;
+
+			/* Request next packet, if required. */
+			if (!dmms[dmm].packet_request)
+				break;
+			if (dmms[dmm].req_timeout_ms || dmms[dmm].req_delay_ms)
+				devc->req_next_at = g_get_monotonic_time() +
+					dmms[dmm].req_delay_ms * 1000;
+			req_packet(sdi, dmm);
 		} else {
 			offset++;
 		}
@@ -108,9 +147,7 @@ static int receive_data(int fd, int revents, int dmm, void *info, void *cb_data)
 {
 	struct sr_dev_inst *sdi;
 	struct dev_context *devc;
-	struct sr_serial_dev_inst *serial;
 	int64_t time;
-	int ret;
 
 	(void)fd;
 
@@ -120,20 +157,13 @@ static int receive_data(int fd, int revents, int dmm, void *info, void *cb_data)
 	if (!(devc = sdi->priv))
 		return TRUE;
 
-	serial = sdi->conn;
-
 	if (revents == G_IO_IN) {
 		/* Serial data arrived. */
 		handle_new_data(sdi, dmm, info);
 	} else {
-		/* Timeout, send another packet request (if DMM needs it). */
-		if (dmms[dmm].packet_request) {
-			ret = dmms[dmm].packet_request(serial);
-			if (ret < 0) {
-				sr_err("Failed to request packet: %d.", ret);
-				return FALSE;
-			}
-		}
+		/* Timeout; send another packet request if DMM needs it. */
+		if (dmms[dmm].packet_request && (req_packet(sdi, dmm) < 0))
+			return FALSE;
 	}
 
 	if (devc->limit_samples && devc->num_samples >= devc->limit_samples) {
diff --git a/hardware/serial-dmm/protocol.h b/hardware/serial-dmm/protocol.h
index f96e43da..fb5a2a33 100644
--- a/hardware/serial-dmm/protocol.h
+++ b/hardware/serial-dmm/protocol.h
@@ -69,6 +69,12 @@ struct dmm_info {
 	uint32_t baudrate;
 	/** Packet size in bytes. */
 	int packet_size;
+	/** Request timeout [ms] before request is considered lost and a new
+	 *  one is sent. Used only if device needs polling. */
+	int64_t req_timeout_ms;
+	/** Delay between reception of packet and next request. Some DMMs
+	 *  need this. Used only if device needs polling. */
+	int64_t req_delay_ms;
 	/** Packet request function. */
 	int (*packet_request)(struct sr_serial_dev_inst *);
 	/** Packet validation function. */
@@ -102,13 +108,20 @@ struct dev_context {
 	/** The current number of already received samples. */
 	uint64_t num_samples;
 
+	/** The starting time of current sampling run. */
 	int64_t starttime;
 
 	uint8_t buf[DMM_BUFSIZE];
 	int bufoffset;
 	int buflen;
+
+	/** The timestamp [µs] to send the next request.
+	 *  Used only if device needs polling. */
+	int64_t req_next_at;
 };
 
+SR_PRIV int req_packet(struct sr_dev_inst *sdi, int dmm);
+
 SR_PRIV int receive_data_BBCGM_M2110(int fd, int revents, void *cb_data);
 SR_PRIV int receive_data_DIGITEK_DT4000ZC(int fd, int revents, void *cb_data);
 SR_PRIV int receive_data_TEKPOWER_TP4000ZC(int fd, int revents, void *cb_data);