diff --git a/src/include/86box/network.h b/src/include/86box/network.h
index 54181ae8e..4f9e6b70e 100644
--- a/src/include/86box/network.h
+++ b/src/include/86box/network.h
@@ -62,6 +62,9 @@
 #define NET_CARD_MAX 4
 #define NET_HOST_INTF_MAX 64
 
+#define NET_PERIOD_10M 0.8
+#define NET_PERIOD_100M 0.08
+
 /* Supported network cards. */
 enum {
     NONE = 0,
@@ -128,6 +131,7 @@ struct _netcard_t {
     mutex_t        *rx_mutex;
     pc_timer_t      timer;
     int             card_num;
+    double          byte_period;
 };
 
 typedef struct {
diff --git a/src/network/net_pcnet.c b/src/network/net_pcnet.c
index 25ced4679..2b2b22540 100644
--- a/src/network/net_pcnet.c
+++ b/src/network/net_pcnet.c
@@ -2025,11 +2025,15 @@ pcnet_bcr_writew(nic_t *dev, uint16_t rap, uint16_t val)
 	case BCR_BSBC:
 	case BCR_EECAS:
 	case BCR_PLAT:
-	case BCR_MIICAS:
 	case BCR_MIIADDR:
 	    dev->aBCR[rap] = val;
 	    break;
 
+	case BCR_MIICAS:
+	    dev->netcard->byte_period = (dev->board == DEV_AM79C973 && (val & 0x28)) ? NET_PERIOD_100M : NET_PERIOD_10M;
+	    dev->aBCR[rap] = val;
+	    break;
+
 	case BCR_STVAL:
 	    val &= 0xffff;
 	    dev->aBCR[BCR_STVAL] = val;
@@ -3055,6 +3059,7 @@ pcnet_init(const device_t *info)
 
     /* Attach ourselves to the network module. */
     dev->netcard = network_attach(dev, dev->aPROM, pcnetReceiveNoSync, pcnetWaitReceiveAvail, pcnetSetLinkState);
+    dev->netcard->byte_period = (dev->board == DEV_AM79C973) ? NET_PERIOD_100M : NET_PERIOD_10M;
 
     timer_add(&dev->timer, pcnetPollTimer, dev, 0);
 
diff --git a/src/network/network.c b/src/network/network.c
index a01eb938e..a8106afeb 100644
--- a/src/network/network.c
+++ b/src/network/network.c
@@ -379,7 +379,7 @@ network_rx_queue(void *priv)
         card->host_drv.notify_in(card->host_drv.priv);
     }
 
-    double timer_period = 0.762939453125 * (rx_bytes > tx_bytes ? rx_bytes : tx_bytes);
+    double timer_period = card->byte_period * (rx_bytes > tx_bytes ? rx_bytes : tx_bytes);
     if (timer_period < 200)
         timer_period = 200;
 
@@ -409,6 +409,7 @@ network_attach(void *card_drv, uint8_t *mac, NETRXCB rx, NETWAITCB wait, NETSETL
     card->tx_mutex = thread_create_mutex();
     card->rx_mutex = thread_create_mutex();
     card->card_num = net_card_current;
+    card->byte_period = NET_PERIOD_10M;
 
     for (int i=0; i<3; i++) {
         network_queue_init(&card->queues[i]);
@@ -440,7 +441,7 @@ network_attach(void *card_drv, uint8_t *mac, NETRXCB rx, NETWAITCB wait, NETSETL
     }
 
     timer_add(&card->timer, network_rx_queue, card, 0);
-    timer_on_auto(&card->timer, 0.762939453125 * 2.0);
+    timer_on_auto(&card->timer, 100);
 
     return card;
 }