diff --git a/devices/video/appleramdac.cpp b/devices/video/appleramdac.cpp
index bc3a7cd..3206f93 100644
--- a/devices/video/appleramdac.cpp
+++ b/devices/video/appleramdac.cpp
@@ -43,7 +43,7 @@ uint16_t AppleRamdac::iodev_read(uint32_t address) {
         case RamdacRegs::PLL_CTRL:
             return this->pll_cr;
         case RamdacRegs::VENDOR_ID:
-            return DACULA_VENDOR_SIERRA;
+            return this->dac_vendor;
         default:
             LOG_F(WARNING, "%s: read from unsupported multi-register at 0x%X",
                   this->name.c_str(), this->dac_addr);
@@ -142,7 +142,15 @@ int AppleRamdac::get_dot_freq() {
     uint8_t p = this->clk_pn[this->pll_cr & 1] >> 5;
     uint8_t n = this->clk_pn[this->pll_cr & 1] & 0x1F;
 
-    double dot_freq = 14318180.0f * (double)m / ((double)n * (double)(1 << p));
+    double dot_freq;
+    if (this->dac_vendor == DACULA_VENDOR_OTHER)
+        dot_freq = 15000000.0f * (double)m / ((double)n + 2) / (double)(1 << p);
+    else if (this->dac_vendor == DACULA_VENDOR_SIERRA)
+        dot_freq = 14318180.0f * (double)m / ((double)n * (double)(1 << p));
+    else {
+        dot_freq = 14318180.0f * (double)m / (double)n / (double)(1 << p);
+        LOG_F(ERROR, "%s: unknown VENDOR_ID", this->name.c_str());
+    }
     return static_cast<int>(dot_freq + 0.5f);
 }
 
diff --git a/devices/video/appleramdac.h b/devices/video/appleramdac.h
index a29c8c2..19c94e9 100644
--- a/devices/video/appleramdac.h
+++ b/devices/video/appleramdac.h
@@ -35,7 +35,8 @@ enum DacFlavour {
     DACULA,
 };
 
-#define DACULA_VENDOR_SIERRA    0x3C
+#define DACULA_VENDOR_SIERRA    0x3C // 14.3 MHz
+#define DACULA_VENDOR_OTHER     0x84 // 15 MHz
 
 constexpr auto VIDEO_XTAL = 14318180.0f; // external crystal oscillator frequency
 
@@ -109,6 +110,7 @@ protected:
     uint8_t     clk_m[2]        = {};
     uint8_t     clk_pn[2]       = {};
     uint8_t     pll_cr          = 0;
+    uint8_t     dac_vendor      = DACULA_VENDOR_SIERRA;
     uint8_t     comp_index      = 0;
     uint8_t     clut_color[3]   = {};
     uint32_t    cursor_clut[8]  = {};