--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/duart28c/src/vsrc/application_block.v	Wed Jul 29 07:08:28 2020 +0000
@@ -0,0 +1,92 @@
+/*
+ * This module encapsulates the application function of our board:
+ * dual UART with 2.8V outputs.
+ */
+
+module application_block (GND, P_3V3, P_2V8, ADBUS, BDBUS);
+
+input GND, P_3V3, P_2V8;
+
+inout [7:0] ADBUS, BDBUS;
+
+/* 2.8V output wires */
+
+wire TxD_2V8_before_R, RTS_2V8_before_R, DTR_2V8_before_R, TxD2_2V8_before_R;
+wire TxD_2V8_after_R, RTS_2V8_after_R, DTR_2V8_after_R, TxD2_2V8_after_R;
+
+/* input signal wires */
+
+wire RxD_in, CTS_in, DSR_in, DCD_in, RI_in, RxD2_in;
+
+/* output buffers */
+
+buffer_ic_common output_buf_common (.Vcc(P_2V8),
+				    .GND(GND),
+				    .nOE1(GND),
+				    .nOE2(GND)
+	);
+
+capacitor output_buf_bypass_cap (P_2V8, GND);
+
+buffer_ic_slot buf_TxD  (.A(ADBUS[0]), .Y(TxD_2V8_before_R));
+buffer_ic_slot buf_RTS  (.A(ADBUS[2]), .Y(RTS_2V8_before_R));
+buffer_ic_slot buf_DTR  (.A(ADBUS[4]), .Y(DTR_2V8_before_R));
+buffer_ic_slot buf_TxD2 (.A(BDBUS[0]), .Y(TxD2_2V8_before_R));
+
+buffer_ic_slot unused_output_buf1 (.A(GND), .Y());
+buffer_ic_slot unused_output_buf2 (.A(GND), .Y());
+buffer_ic_slot unused_output_buf3 (.A(GND), .Y());
+buffer_ic_slot unused_output_buf4 (.A(GND), .Y());
+
+/* output series resistors */
+
+resistor TxD_series_R (TxD_2V8_before_R, TxD_2V8_after_R);
+resistor RTS_series_R (RTS_2V8_before_R, RTS_2V8_after_R);
+resistor DTR_series_R (DTR_2V8_before_R, DTR_2V8_after_R);
+resistor TxD2_series_R (TxD2_2V8_before_R, TxD2_2V8_after_R);
+
+/* input buffers */
+
+buffer_ic_common input_buf_common (.Vcc(P_3V3),
+				   .GND(GND),
+				   .nOE1(GND),
+				   .nOE2(GND)
+	);
+
+capacitor input_buf_bypass_cap (P_3V3, GND);
+
+buffer_ic_slot buf_RxD  (.A(RxD_in),  .Y(ADBUS[1]));
+buffer_ic_slot buf_CTS  (.A(CTS_in),  .Y(ADBUS[3]));
+buffer_ic_slot buf_DSR  (.A(DSR_in),  .Y(ADBUS[5]));
+buffer_ic_slot buf_DCD  (.A(DCD_in),  .Y(ADBUS[6]));
+buffer_ic_slot buf_RI   (.A(RI_in),   .Y(ADBUS[7]));
+buffer_ic_slot buf_RxD2 (.A(RxD2_in), .Y(BDBUS[1]));
+
+buffer_ic_slot unused_input_buf1 (.A(GND), .Y());
+buffer_ic_slot unused_input_buf2 (.A(GND), .Y());
+
+/* input pull-up resistors */
+
+resistor RxD_pullup (RxD_in, P_2V8);
+resistor CTS_pullup (CTS_in, P_2V8);
+resistor DSR_pullup (DSR_in, P_2V8);
+resistor DCD_pullup (DCD_in, P_2V8);
+resistor RI_pullup  (RI_in,  P_2V8);
+resistor RxD2_pullup (RxD2_in, P_2V8);
+
+/* target interface headers */
+
+target_if target_if (	.GND(GND),
+			.UART0_TxD(TxD_2V8_after_R),
+			.UART0_RxD(RxD_in),
+			.UART0_RTS(RTS_2V8_after_R),
+			.UART0_CTS(CTS_in),
+			.UART0_DTR(DTR_2V8_after_R),
+			.UART0_DSR(DSR_in),
+			.UART0_DCD(DCD_in),
+			.UART0_RI(RI_in),
+			.UART1_TxD(TxD2_2V8_after_R),
+			.UART1_RxD(RxD2_in)
+	);
+
+endmodule