diff --git a/regs/systembus_bits.csv b/regs/systembus_bits.csv
index 5eea483..310596b 100644
--- a/regs/systembus_bits.csv
+++ b/regs/systembus_bits.csv
@@ -60,3 +60,8 @@
 "FFST",,"5","holly_cpu_if_block_internal_write_buffer",,,
 "FFST",,"4","holly_g2_if_block_internal_write_buffer",,,
 "FFST",,"0","aica_internal_write_buffer",,,
+,,,,,,
+"ISTEXT",,3,"external_device",1,,
+"ISTEXT",,2,"modem",1,,
+"ISTEXT",,1,"aica",1,,
+"ISTEXT",,0,"gdrom",1,,
diff --git a/regs/systembus_bits.ods b/regs/systembus_bits.ods
index a0baeb0..20fade0 100644
Binary files a/regs/systembus_bits.ods and b/regs/systembus_bits.ods differ
diff --git a/systembus_bits.hpp b/systembus_bits.hpp
index 9438840..80fce39 100644
--- a/systembus_bits.hpp
+++ b/systembus_bits.hpp
@@ -131,3 +131,13 @@ constexpr uint32_t holly_g2_if_block_internal_write_buffer(uint32_t reg) { retur
 constexpr uint32_t aica_internal_write_buffer(uint32_t reg) { return (reg >> 0) & 0x1; }
 }
 
+namespace istext {
+constexpr uint32_t external_device = 1 << 3;
+constexpr uint32_t modem = 1 << 2;
+
+constexpr uint32_t aica = 1 << 1;
+
+constexpr uint32_t gdrom = 1 << 0;
+
+}
+